Mesogenic media and liquid crystal display

ABSTRACT

The invention relates to mesogenic media comprising
     a first component, component A, consisting of bimesogenic compounds selected from the group of compounds of formulae A-I to A-III   

     
       
         
         
             
             
         
       
         
         a second component, component B, consisting of nematogenic compounds, preferably selected from the group of compounds of formulae B-I to B-III 
       
    
     
       
         
         
             
             
         
       
         
         and 
         a third component, component C, consisting of one or more chiral molecules, 
         wherein the parameters have the meaning given in claim  1 , to the use of mesogenic media in flexoelectric liquid crystal devices and to those devices comprising a liquid crystal medium according to the present invention.

The invention relates to mesogenic media comprising

a first component, component A, consisting of bimesogenic compoundsselected from the group of compounds of formulae A-I to A-III

wherein the parameters have the meaning given herein below,a second component, component B, consisting of nematogenic compounds,anda third component, component C, consisting of one or more chiralmolecules,to the use of these mesogenic media in liquid crystal devices and inparticular in flexoelectric liquid crystal devices, as well as to liquidcrystal devices comprising a liquid crystal medium according to thepresent invention.

Bimesogenic compounds are also known as called “dimeric liquidcrystals”.

This invention particularly concerns a general method for improving theswitching speed of liquid crystalline mixtures developed for modes thatutilize the flexoelectric effect.

Liquid Crystal Displays (LCDs) are widely used to display information.LCDs are used for direct view displays, as well as for projection typedisplays. The electro-optical mode which is employed for most displaysstill is the twisted nematic (TN)-mode with its various modifications.Besides this mode, the super twisted nematic (STN)-mode and morerecently the optically compensated bend (OCB)-mode and the electricallycontrolled birefringence (ECB)-mode with their various modifications, ase. g. the vertically aligned nematic (VAN), the patterned ITO verticallyaligned nematic (PVA)-, the polymer stabilized vertically alignednematic (PSVA)-mode and the multi domain vertically aligned nematic(MVA)-mode, as well as others, have been increasingly used. All thesemodes use an electrical field, which is substantially perpendicular tothe substrates, respectively to the liquid crystal layer. Besides thesemodes there are also electro-optical modes employing an electrical fieldsubstantially parallel to the substrates, respectively the liquidcrystal layer, like e.g. the In Plane Switching (short IPS) mode (asdisclosed e.g. in DE 40 00 451 and EP 0 588 568) and the Fringe FieldSwitching (FFS) mode. Especially the latter mentioned electro-opticalmodes, which have good viewing angle properties and improved responsetimes, are increasingly used for LCDs for modern desktop monitors andeven for displays for TV and for multimedia applications and thus arecompeting with the TN-LCDs.

Further to these displays, new display modes using cholesteric liquidcrystals having a relatively short cholesteric pitch have been proposedfor use in displays exploiting the so called “flexo-electric” effect.The term “liquid crystal”, “mesomorphic compound”, or “mesogeniccompound” (also shortly referred to as “mesogen”) means a compound thatunder suitable conditions of temperature, pressure and concentration canexist as a mesophase (nematic, smectic, etc.) or in particular as a LCphase. Non-amphiphilic mesogenic compounds comprise for example one ormore calamitic, banana-shaped or discotic mesogenic groups.

Flexoelectric liquid crystal materials are known in prior art. Theflexoelectric effect is described inter alia by Chandrasekhar, “LiquidCrystals”, 2nd edition, Cambridge University Press (1992) and P. G.deGennes et al., “The Physics of Liquid Crystals”, 2nd edition, OxfordScience Publications (1995).

In these displays the cholesteric liquid crystals are oriented in the“uniformly lying helix” arrangement (ULH), which also give this displaymode its name. For this purpose, a chiral substance which is mixed witha nematic material induces a helical twist transforming the materialinto a chiral nematic material, which is equivalent to a cholestericmaterial. The term “chiral” in general is used to describe an objectthat is non-superimposable on its mirror image. “Achiral” (non-chiral)objects are objects that are identical to their mirror image. The termschiral nematic and cholesteric are used synonymously in thisapplication, unless explicitly stated otherwise. The pitch induced bythe chiral substance (P₀) is in a first approximation inverselyproportional to the concentration (c) of the chiral material used. Theconstant of proportionality of this relation is called the helicaltwisting power (HTP) of the chiral substance and defined by equation (1)

HTP≡1/(c·P ₀)  (1)

wherein

-   c is concentration of the chiral compound.

The uniform lying helix texture is realized using a chiral nematicliquid crystal with a short pitch, typically in the range from 0.2 μm to1 μm, preferably of 1.0 μm or less, in particular of 0.5 μm or less,which is unidirectional aligned with its helical axis parallel to thesubstrates, e. g. glass plates, of a liquid crystal cell. In thisconfiguration the helical axis of the chiral nematic liquid crystal isequivalent to the optical axis of a birefringent plate.

If an electrical field is applied to this configuration normal to thehelical axis the optical axis is rotated in the plane of the cell,similar as the director of a ferroelectric liquid crystal rotate as in asurface stabilized ferroelectric liquid crystal display. Theflexoelectric effect is characterized by fast response times typicallyranging from 6 μs to 100 μs. It further features excellent grey scalecapability.

The field induces a splay bend structure in the director which isaccommodated by a tilt in the optical axis. The angle of the rotation ofthe axis is in first approximation directly and linearly proportional tothe strength of the electrical field. The optical effect is best seenwhen the liquid crystal cell is placed between crossed polarizers withthe optical axis in the unpowered state at an angle of 22.5° to theabsorption axis of one of the polarizers. This angle of 22.5° is alsothe ideal angle of rotation of the electric field, as thus, by theinversion the electrical field, the optical axis is rotated by 45° andby appropriate selection of the relative orientations of the preferreddirection of the axis of the helix, the absorption axis of the polarizerand the direction of the electric field, the optical axis can beswitched from parallel to one polarizer to the center angle between bothpolarizers. The optimum contrast is then achieved when the total angleof the switching of the optical axis is 45°. In that case thearrangement can be used as a switchable quarter wave plate, provided theoptical retardation, i. e. the product of the effective birefringence ofthe liquid crystal and the cell gap, is selected to be the quarter ofthe wave length. In this context the wavelength referred to is 550 nm,the wavelength for which the sensitivity of the human eye is highest,unless explicitly stated otherwise.

The angle of rotation of the optical axis (Φ) is given in goodapproximation by formula (2)

tan Φ=ēP ₀ E/(2πK)  (2)

wherein

-   P₀ is the undisturbed pitch of the cholesteric liquid crystal,-   ē is the average [ē=½(e_(splay)+e_(bend))] of the splay    flexoelectric coefficient (e_(splay)) and the bend flexoelectric    coefficient (e_(bend)),-   E is the electrical field strength and-   K is the average [K=½(k₁₁+k₃₃)] of the splay elastic constant (k₁₁)    and the bend elastic constant (K₃₃)    and wherein-   ē/K is called the flexo-elastic ratio.

This angle of rotation is half the switching angle in a flexoelectricswitching element.

The response time (τ) of this electro-optical effect is given in goodapproximation by formula (3)

τ=[P ₀/(2π)]² γ/K  (3)

wherein

-   γ is the effective viscosity coefficient associated with the    distortion of the helix.

There is a critical field (E_(c)) to unwind the helix, which can beobtained from equation (4)

E _(c)=(π² /P ₀)·[k ₂₂/(∈₀·Δ∈)]^(1/2)  (4)

wherein

-   k₂₂ is the twist elastic constant,-   ∈₀ is the permittivity of vacuum and-   Δ∈ is the dielectric anisotropy of the liquid crystal.

In this mode, however several problems still have to be resolved, whichare, amongst others, difficulties in obtaining the required uniformorientation, an unfavorably high voltage required for addressing, whichis incompatible with common driving electronics, a not really dark “offstate”, which deteriorates the contrast, and, last not least, apronounced hysteresis in the electro-optical characteristics.

A relatively new display mode, the so-called “uniformly standing helix”(USH) mode, may be considered as an alternative mode to succeed the IPS,as it can show improved black levels, even compared to other displaymode providing wide viewing angles (e.g. IPS, VA etc.).

For the USH mode, like for the ULH mode, flexoelectric switching hasbeen proposed, using bimesogenic liquid crystal materials. Bimesogeniccompounds are known in general from prior art (cf. also Hori, K.,Iimuro, M., Nakao, A., Toriumi, H., J. Mol. Struc. 2004, 699, 23-29).The term “bimesogenic compound” relates to compounds comprising twomesogenic groups in the molecule. Just like normal mesogens they canform many mesophases, depending on their structure. In particularcompounds of formula A-II induce a second nematic phase, when added to anematic liquid crystal medium.

The term “mesogenic group” means in this context, a group with theability to induce liquid crystal (LC) phase behaviour. The compoundscomprising mesogenic groups do not necessarily have to exhibit an LCphase themselves. It is also possible that they show LC phase behaviouronly in mixtures with other compounds. For the sake of simplicity, theterm “liquid crystal” is used hereinafter for both mesogenic and LCmaterials.

However, due to the unfavorably high driving voltage required, to therelatively narrow phase range of the chiral nematic materials and totheir irreversible switching properties, materials from prior art arenot compatible for the use with current LCD driving schemes.

For displays of the USH and ULH mode, new liquid crystalline media withimproved properties are required. Especially the birefringence (Δn)should be optimized for the optical mode. The birefringence Δn herein isdefined in equation (5)

Δn=n _(e) −n _(o)  (5)

wherein n_(e) is the extraordinary refractive index and n_(o) is theordinary refractive index, and the average refractive index n_(av.) isgiven by the following equation (6).

n _(av.)=[(2n _(o) ² +n _(e) ²)/3]^(1/2)  (6)

The extraordinary refractive index n_(e) and the ordinary refractiveindex n_(o) can be measured using an Abbe refractometer. An can then becalculated from equation (5).

Furthermore, for displays utilizing the USH or ULH mode the opticalretardation d*Δn (effective) of the liquid crystal media shouldpreferably be such that the equation (7)

sin 2(π·d·Δn/λ)=1  (7)

wherein

-   d is the cell gap and-   λ is the wave length of light    is satisfied. The allowance of deviation for the right hand side of    equation (7) is +/−3%.

The wave length of light generally referred to in this application is550 nm, unless explicitly specified otherwise.

The cell gap of the cells preferably is in the range from 1 μm to 20 μm,in particular within the range from 2.0 μm to 10 μm.

For the ULH/USH mode, the dielectric anisotropy (Δ∈) should be as smallas possible, to prevent unwinding of the helix upon application of theaddressing voltage. Preferably Δ∈ should be slightly higher than 0 andvery preferably be 0.1 or more, but preferably 10 or less, morepreferably 7 or less and most preferably 5 or less. In the presentapplication the term “dielectrically positive” is used for compounds orcomponents with Δ∈>3.0, “dielectrically neutral” with −1.5≦Δ∈≦3.0 and“dielectrically negative” with Δ∈<−1.5. Δ∈ is determined at a frequencyof 1 kHz and at 20° C. The dielectric anisotropy of the respectivecompound is determined from the results of a solution of 10% of therespective individual compound in a nematic host mixture. In case thesolubility of the respective compound in the host medium is less than10% its concentration is reduced by a factor of 2 until the resultantmedium is stable enough at least to allow the determination of itsproperties. Preferably the concentration is kept at least at 5%,however, in order to keep the significance of the results a high aspossible. The capacitance of the test mixtures are determined both in acell with homeotropic and with homogeneous alignment. The cell gap ofboth types of cells is approximately 20 μm. The voltage applied is arectangular wave with a frequency of 1 kHz and a root mean square valuetypically of 0.5 V to 1.0 V, however, it is always selected to be belowthe capacitive threshold of the respective test mixture.

Δ∈ is defined as (∈_(∥)−∈_(⊥)), whereas ∈_(av.) is (∈_(∥)+2∈_(⊥))/3. Thedielectric permittivity of the compounds is determined from the changeof the respective values of a host medium upon addition of the compoundsof interest. The values are extrapolated to a concentration of thecompounds of interest of 100%. The host mixture is disclosed in H. J.Coles et al., J. Appl. Phys. 2006, 99, 034104 and has the compositiongiven in the table 1.

TABLE 1 Host mixture composition Compound Concentration F-PGI-ZI-9-ZGP-F25% F-PGI-ZI-11-ZGP-F 25% FPGI-O-5-O-PP-N 9.5% FPGI-O-7-O-PP-N 39% CD-11.5%

Besides the above mentioned parameters, the media have to exhibit asuitably wide range of the nematic phase, a rather small rotationalviscosity and an at least moderately high specific resistivity.

Similar liquid crystal compositions with short cholesteric pitch forflexoelectric devices are known from EP 0 971 016, GB 2 356 629 andColes, H. J., Musgrave, B., Coles, M. J., and Willmott, J., J. Mater.Chem., 11, p. 2709-2716 (2001). EP 0 971 016 reports on mesogenicestradiols, which, as such, have a high flexoelectric coefficient. GB 2356 629 suggests the use of bimesogenic compounds in flexoelectricdevices. The flexoelectric effect herein has been investigated in purecholesteric liquid crystal compounds and in mixtures of homologouscompounds only so far. Most of these compounds were used in binarymixtures consisting of a chiral additive and a nematic liquid crystalmaterial being either a simple, conventional monomesogenic material or abimesogenic one. These materials do have several drawbacks for practicalapplications, like insufficiently wide temperature ranges of the chiralnematic—or cholesteric phase, too small flexoelectric ratios, smallangles of rotation.

One aim of the invention was to provide improved flexoelectric devicesthat exhibit high switching angles and fast response times. Another aimwas to provide liquid crystal materials with advantageous properties, inparticular for use in flexoelectric displays that enable good uniformalignment over the entire area of the display cell without the use of amechanical shearing process, good contrast, high switching angles andfast response times also at low temperatures. The liquid crystalmaterials should exhibit low melting points, broad chiral nematic phaseranges, short temperature independent pitch lengths and highflexoelectric coefficients.

It is well known that flexoelectric-optic effects can be used as modesfor liquid crystal displays. The most common examples of such effectsare the ULH and USH effects. The ULH mode was originally described byMeyer and Patel in 1987 (J. S. Patel, R. B. Meyer, Phys. Rev. Lett.,1987, 58, 1538), and further work in this field is described in Rudquistet al in 1997 (P. Rudquist and S. T. Largerwall, Liquid Crystal 1997,23, 503). Materials that can be used for this mode is e.g. disclosed inGB 23 56 629. A paper outlining the properties of flexo mixturescomposed primarily of bimesogens was published by Coles et al (H. J.Coles, a M. J. Clarke, S. M. Morris, b B. J. Broughton, and A. E.Blatch, J. of Applied Physics 2006, 99, 034104) in which the switchingspeed of ULH mixtures is discussed in some detail.

It is known that the use of bimesogens having alkylene spacer groups andsimilar bimesogens exhibit a lower temperature phase below a nematicphase. This phase has been assigned to a twist bend nematic phase, seee.g. Luckhurst et al., 2011 Physical Review E 2011, 84, 031704. Whenlooking to exploit the flexoelectric properties of mixtures ofbimesogens the twist bend nematic phase can restrict the lower workingtemperature of the mixtures. The addition of small amounts of low molarmass liquid crystal, in addition to increasing the switching speed, canbe used to reduce the temperature to the twist bend phase while at thesame time allowing the use of this phase, respectively of its thepre-transitional effects, to increase the desirable properties of thesemixtures as described in not yet laid open patent application EP 11 0054 89.7.

It has also been found that aligning liquid crystals in the ULH mode isdifficult, and an alternative flexoelectric-optic mode, the USH mode wasproposed by Coles et al in WO2006/003441, and in SID2009 (F. Castles, S.M. Morris, and H. J. Coles, SID 09 DIGEST, 2009, 582) as well as inColes et al 2011 (D. J. Gardiner, S. M. Morris, F. Castles, M. M. Qasim,W. S. Kim, S S. Choi, H. J. Park, I. J. Chung, H. J. Coles, AppliedPhysics Letter, 2011, 98, 263508). The material requirements for bothULH and USH are similar. Recently, the Coles group published a paper onthe structure-property relationship for dimeric liquid crystals. Coleset al., 2012 (Physical Review E 2012, 85, 012701).

One drawback of flexoelectric liquid crystal devices is theirinsufficient response time. Several papers and patents describemixtures, which have a switching time of less than 1 ms, however in mostcases the switching times are quoted at temperature well above ambienttemperature, or the voltage required to achieve this switching speed isrelatively high. The materials used in these mixtures tend to bebimesogens. One of the drawbacks of the use of these compounds is thatin some cases the switching speeds are slow especially at temperatureclose to ambient. The reason for this is believed to be related to thehigh viscosity of the mixtures at ambient temperature. As will bediscussed later, theory indicates that viscosity is an importantvariable in the equations that describe the switching speed of chiralflexo modes such as the Uniform Lying Helix and the Uniform StandingHelix modes. It's not clear from the literature which viscosity this is,but it is believed to be the rotational viscosity (γ₁).

One aim of this invention is to provide mixtures for displays designedfor modes that exploit the flexoelectric effect consisting predominantlyof bimesogens and showing improved switching speed, achieved orachievable by use liquid crystals exhibiting of low rotational viscosityin combination with more conventional bimesogens.

Another aim of the present invention is to provide mixtures for suchdisplays showing significantly improved properties by the use ofspecially selected bimesogens.

In liquid crystal displays exploiting the flexoelectric modes the tiltangle (Θ) describes the rotation of the optic axis in the x-y plane ofthe cell. There are two basic methods of using this effect to generate awhite and dark state. The biggest difference between these two methodsresides in the tilt angle that is required and in the orientation of thetransmission axis of the polariser relative the optic axis for the ULHin the zero field state. The two different methods are briefly describedbelow with reference to FIGS. 1 and 2.

The main difference between the “Θ mode” (illustrated in FIG. 2) and the“2Θ mode” (shown in FIG. 1) is that the optical axis of the liquidcrystal in the state at zero field is either parallel to one of thepolariser axis (in the case of the 2Θ mode) or at an angle of 22.5° toaxis one of the polarisers (in the case of the Θ mode). The advantage ofthe 2Θ mode over the Θ mode is that the liquid crystal display appearsblack when there is no field applied to the cell. The advantage of the Θmode, however, is that e/K may be lower because only half of theswitching angle is required for this mode compared to the 2Θ mode.

Comparing the switching speed of ULH mixtures it is important to alsoknow the switching angle associated with the respective effect.

The other mixture variables should also be considered. Highertemperature usually leads to faster switching times, usually because theviscosity of the mixture decreases. The field used is also important.Faster switching speed can usually be achieved with higher fields in ULHflexoelectric mode.

Yet another factor which has to be considered are the details of theswitching mode. Contrary to most commercial LC mode, the ULH T_(off)time can be driven, therefore there are at least two possible switchingregimes:

Switching time=T _(on) +T _(off(driven))

Switching time=T _(on) +T _(off(non-driven))

If both switching on and switching off are driven the response times aremuch shorter, typically in the range of 2 ms compared to 5 ms.

The present invention allows to reduce the switching times in both ofthese regimes by adding additives having a low rotational viscosity.

As already mentioned above the present invention discloses a method ofimproving the switching speed of chiral flexo mixtures. It has beenreported in the literature that the relaxation switching time of suchmixtures can be described by the following equation

${\tau = {\frac{\gamma}{K}\frac{p^{2}}{{4\; \pi^{2}}}}},$

Where γ is the “effective viscosity associated with the distortion ofthe helix” (Coles et al 2006). Furthermore in a paper from Coles et al.(B Musgrave, P. Lehmann, H. J. Coles, Liquid Crystals, (1999), 28 (8),1235) the viscosity term is referred to as γ₁.

E.g. in J. Appl. Phys. 99, 034104 (2006) it is shown that the switchingspeed of a mixture of bimesogens mixture increases significantly withdecreasing temperature. Though this can be counteracted to a certaindegree by increasing the field applied the switching speed is stilllonger at lower temperature compared to higher temperatures.

This invention shows that the addition of viscosity modifiers canimprove the switching speed of mixtures containing dimers. Surprisinglyeven a small amount of a viscosity modifier can have a very large effecton the speed of switching. In addition the use of these compounds alsolowers the temperature of the nematic to second nematic (twist bend)phase or other phases and reduces melting points and may also be used toincrease the clearing point of the mixture.

Liquid crystalline media comprising both bimesogens and nematogens aredisclosed in GB 2 387 603. However these media have relatively lowvalues of the flexoelectric ratio e/K.

Other aims of the present invention are immediately evident to theperson skilled in the art from the following detailed description.

The inventors have found out that the above aims can be surprisinglyachieved by providing bimesogenic compounds according to the presentinvention. These compounds, when used in chiral nematic liquid crystalmixtures, lead to low melting points, broad chiral nematic phases. Inparticular, they exhibit relatively high values of the elastic constantk₁₁, low values of the bend elastic constant k₃₃ and high values of theflexoelectric coefficient.

The present invention relates to mesogenic materials comprising

a first component, component A, consisting of bimesogenic compoundsselected from the group of compounds of formulae A-I to A-III

wherein

-   R¹¹ and R¹², R²¹ and R²² and R³¹ and R³² are each independently H,    F, Cl, CN, NCS or a straight-chain or branched alkyl group with 1 to    25 C atoms which may be unsubstituted, mono- or polysubstituted by    halogen or CN, it being also possible for one or more non-adjacent    CH₂ groups to be replaced, in each occurrence independently from one    another, by —O—, —S—, —NH—, —N(CH₃)—, —CO—, —COO—, —OCO—, —O—CO—O—,    —S—CO—, —CO—S—, —CH═CH—, —CH═CF—, —CF═CF— or —C≡C— in such a manner    that oxygen atoms are not linked directly to one another,-   MG¹¹ and MG¹², MG²¹ and MG²² and MG³¹ and MG³² are each    independently a mesogenic group,-   Sp¹, Sp² and Sp³ are each independently a spacer group comprising 5    to 40 C atoms, wherein one or more non-adjacent CH₂ groups, with the    exception of the CH₂ groups of Sp¹ linked to O-MG¹¹ and/or O-MG¹²,    of Sp² linked to MG²¹ and/or MG²² and of Sp³ linked to X³¹ and X³²,    may also be replaced by —O—, —S—, —NH—, —N(CH₃)—, —CO—, —O—CO—,    —S—CO—, —O—COO—, —CO—S—, —CO—O—, —CH(halogen)-, —CH(CN)—, —CH═CH— or    —C≡C—, however in such a way that (in the molecules?) no two O-atoms    are adjacent to one another, no two —CH═CH— groups are adjacent to    each other, and no two groups selected from —O—CO—, —S—CO—, —O—COO—,    —CO—S—, —CO—O— and —CH═CH— are adjacent to each other and-   X³¹ and X³² are independently from one another a linking group    selected from —CO—O—, —O—CO—, —CH═CH—, —C═C—, —C≡C— or —S—, and,    alternatively, one of them may also be either —O— or a single bond,    and, again alternatively, one of them may be —O— and the other one a    single bond,    a second component, component B, consisting of nematogenic    compounds, preferably selected from the group of compounds of    formulae B-I to B-III

wherein

-   R^(B1), R^(B21) and R^(B22) and R^(B31) and R^(B32) are each    independently H, F, Cl, CN, NCS or a straight-chain or branched    alkyl group with 1 to 25 C atoms which may be unsubstituted, mono-    or polysubstituted by halogen or CN, it being also possible for one    or more non-adjacent CH₂ groups to be replaced, in each occurrence    independently from one another, by —O—, —S—, —NH—, —N(CH₃)—, —CO—,    —COO—, —OCO—, —O—CO—O—, —S—CO—, —CO—S—, —CH═CH—, —CH═CF—, —CF═CF— or    —C≡C— in such a manner that oxygen atoms are not linked directly to    one another,-   X^(B1) is F, Cl, CN, NCS, preferably CN,-   Z^(B1), Z^(B2) and Z^(B3) are in each occurrence independently    —CH₂—CH₂—, —CO—O—, —O—CO—, —CF₂—O—, —O—CF₂—, —CH═CH— or a single    bond, preferably —CH₂—CH₂—, —CO—O—, —CH═CH— or a single bond, more    preferably —CH₂—CH₂— or a single bond, even more preferably one of    the groups present in one compound is —CH₂—CH₂— and the others are a    single bond, most preferably all are a single bond,

and

are in each occurrence independently

or

preferably

or

most preferably

alternatively one or more of

are

and

-   n is 1, 2 or 3, preferably 1 or 2,    and    a third component, component C, consisting of one or more chiral    molecules.

The chiral compounds of component C are preferably selected from thegroup of compounds of formulae C-I to C-III

Especially preferred for component C are chiral compounds, also calledchiral dopants selected from formulae C-I to and C-III,

the latter ones including the respective (S,S) enantiomers, wherein Eand F are each independently 1,4-phenylene or trans-1,4-cyclohexylene, vis 0 or 1, Z⁰ is —COO—, —OCO—, —CH₂CH₂— or a single bond, and R isalkyl, alkoxy or alkanoyl with 1 to 12 C atoms.

Preferably used are compounds of formulae A-I to A-III wherein

-   Sp¹, Sp² and Sp³ are each independently —(CH₂)_(n)— with-   n an integer from 1 to 15, most preferably an uneven integer,    wherein one or more —CH₂— groups may be replaced by —CO—.

Especially preferably used are compounds of formula A-III wherein

-   —X³¹-Sp³-X³²— is -Sp³-O—, -Sp³-CO—O—, -Sp³-O—CO—, —O-Sp³-,    —O-Sp³-CO—O—, —O-Sp³-O—CO—, —O—CO-Sp³-O—, —O—CO-Sp³-O—CO—,    —CO—O-Sp³-O— or —CO—O-Sp³-CO—O—, however under the condition that in    —X³¹-Sp³-X³²— no two O-atoms are adjacent to one another, no two    —CH═CH— groups are adjacent to each other and no two groups selected    from —O—CO—, —S—CO—, —O—OCO—, —CO—S—, —CO—O— and —CH═CH— are    adjacent to each other.

Preferably used are compounds of formula A-I in which

-   MG¹¹ and MG¹² are independently from one another -A¹¹-(Z¹-A¹²)_(m)-    wherein-   Z¹ is —COO—, —OCO—, —O—CO—O—, —OCH₂—, —CH₂O—, —CH₂CH₂—, —(CH₂)₄—,    —CF₂CF₂—, —CH═CH—, —CF═CF—, —CH═CH—OCO—, —OCO—CH═CH—, —C≡C— or a    single bond,-   A¹¹ and A¹² are each independently in each occurrence 1,4-phenylene,    wherein in addition one or more CH groups may be replaced by    N,trans-1,4-cyclo-hexylene in which, in addition, one or two    non-adjacent CH₂ groups may be replaced by O and/or S,    1,4-cyclohexenylene, 1,4-bicyclo-(2,2,2)-octylene,    piperidine-1,4-diyl, naphthalene-2,6-diyl,    decahydro-naphthalene-2,6-diyl,    1,2,3,4-tetrahydro-naphthalene-2,6-diyl, cyclobutane-1,3-diyl,    spiro[3.3]heptane-2,6-diyl or dispiro[3.1.3.1]decane-2,8-diyl, it    being possible for all these groups to be unsubstituted, mono-, di-,    tri- or tetrasubstituted with F, Cl, CN or alkyl, alkoxy,    alkylcarbonyl or alkoxycarbonyl groups with 1 to 7 C atoms, wherein    one or more H atoms may be substituted by F or Cl, and-   m is 0, 1, 2 or 3.

Preferably used are compounds of formula A-II in which

-   MG²¹ and MG²² are independently from one another -A²¹-(Z²-A²²)_(m)-    wherein-   Z² is —COO—, —OCO—, —O—CO—O—, —OCH₂—, —CH₂O—, —CH₂CH₂—, —(CH₂)₄—,    —CF₂CF₂—, —CH═CH—, —CF═CF—, —CH═CH—OCO—, —OCO—CH═CH—, —C≡C— or a    single bond,-   A²¹ and A²² are each independently in each occurrence 1,4-phenylene,    wherein in addition one or more CH groups may be replaced by    N,trans-1,4-cyclo-hexylene in which, in addition, one or two    non-adjacent CH₂ groups may be replaced by O and/or S,    1,4-cyclohexenylene, 1,4-bicyclo-(2,2,2)-octylene,    piperidine-1,4-diyl, naphthalene-2,6-diyl,    decahydro-naphthalene-2,6-diyl,    1,2,3,4-tetrahydro-naphthalene-2,6-diyl, cyclobutane-1,3-diyl,    spiro[3.3]heptane-2,6-diyl or dispiro[3.1.3.1]decane-2,8-diyl, it    being possible for all these groups to be unsubstituted, mono-, di-,    tri- or tetrasubstituted with F, Cl, CN or alkyl, alkoxy,    alkylcarbonyl or alkoxycarbonyl groups with 1 to 7 C atoms, wherein    one or more H atoms may be substituted by F or Cl, and-   m is 0, 1, 2 or 3.

Most preferably used are compounds of formula A-III in which

-   MG³¹ and MG³² are independently from one another -A³¹-(Z³-A³²)_(m)-    wherein-   Z³ is —COO—, —OCO—, —O—CO—O—, —OCH₂—, —CH₂O—, —CH₂CH₂—, —(CH₂)₄—,    —CF₂CF₂—, —CH═CH—, —CF═CF—, —CH═CH—OCO—, —OCO—CH═CH—, —C≡C— or a    single bond,-   A³¹ and A³² are each independently in each occurrence 1,4-phenylene,    wherein in addition one or more CH groups may be replaced by    N,trans-1,4-cyclo-hexylene in which, in addition, one or two    non-adjacent CH₂ groups may be replaced by O and/or S,    1,4-cyclohexenylene, 1,4-bicyclo-(2,2,2)-octylene,    piperidine-1,4-diyl, naphthalene-2,6-diyl,    decahydro-naphthalene-2,6-diyl,    1,2,3,4-tetrahydro-naphthalene-2,6-diyl, cyclobutane-1,3-diyl,    spiro[3.3]heptane-2,6-diyl or dispiro[3.1.3.1]decane-2,8-diyl, it    being possible for all these groups to be unsubstituted, mono-, di-,    tri- or tetrasubstituted with F, Cl, CN or alkyl, alkoxy,    alkylcarbonyl or alkoxycarbonyl groups with 1 to 7 C atoms, wherein    one or more H atoms may be substituted by F or Cl, and-   m is 0, 1, 2 or 3.

Preferably the compounds of formula A-III are unsymmetric compounds,preferably having different mesogenic groups MG³¹ and MG³².

Generally preferred are compounds of formulae A-I to A-III in which thedipoles of the ester groups present in the mesogenic groups are alloriented in the same direction, i.e. all —CO—O— or all —O—CO—.

Especially preferred are compounds of formulae A-I and/or A-II and/orA-III wherein the respective pairs of mesogenic groups (MG¹¹ and MG¹²)and (MG²¹ and MG²²) and (MG³¹ and MG³²) at each occurrence independentlyfrom each other comprise one, two or three six-atomic rings, preferablytwo or three six-atomic rings.

A smaller group of preferred mesogenic groups of formula II is listedbelow. For reasons of simplicity, Phe in these groups is 1,4-phenylene,PheL is a 1,4-phenylene group which is substituted by 1 to 4 groups L,with L being preferably F, Cl, CN, OH, NO₂ or an optionally fluorinatedalkyl, alkoxy or alkanoyl group with 1 to 7 C atoms, very preferably F,Cl, CN, OH, NO₂, CH₃, C₂H₅, OCH₃, OC₂H₅, COCH₃, COC₂H₅, COOCH₃, COOC₂H₅,CF₃, OCF₃, OCHF₂, OC₂F₅, in particular F, Cl, CN, CH₃, C₂H₅, OCH₃, COCH₃and OCF₃ most preferably F, Cl, CH₃, OCH₃ and COCH₃ and Cyc is1,4-cyclohexylene. This list comprises the sub-formulae shown below aswell as their mirror images

-Phe-Z-Phe-  II-1

-Phe-Z-Cyc-  II-2

-Cyc-Z-Cyc-  II-3

-PheL-Z-Phe-  II-4

-PheL-Z-Cyc-  II-5

-PheL-Z-PheL-  II-6

-Phe-Z-Phe-Z-Phe-  II-7

-Phe-Z-Phe-Z-Cyc-  II-8

-Phe-Z-Cyc-Z-Phe-  II-9

-Cyc-Z-Phe-Z-Cyc-  II-10

-Phe-Z-Cyc-Z-Cyc-  II-11

-Cyc-Z-Cyc-Z-Cyc-  II-12

-Phe-Z-Phe-Z-PheL-  II-13

-Phe-Z-PheL-Z-Phe-  II-14

-PheL-Z-Phe-Z-Phe-  II-15

-PheL-Z-Phe-Z-PheL-  II-16

-PheL-Z-PheL-Z-Phe-  II-17

-PheL-Z-PheL-Z-PheL-  II-18

-Phe-Z-PheL-Z-Cyc-  II-19

-Phe-Z-Cyc-Z-PheL-  II-20

-Cyc-Z-Phe-Z-PheL-  II-21

-PheL-Z-Cyc-Z-PheL-  II-22

-PheL-Z-PheL-Z-Cyc-  II-23

-PheL-Z-Cyc-Z-Cyc-  II-24

-Cyc-Z-PheL-Z-Cyc-  II-25

Particularly preferred are the subformulae II-1, II-4, II-6, II-7,II-13, II-14, II-15, II-16, II-17 and II-18.

In these preferred groups Z in each case independently has one of themeanings of Z¹ as given in formula II. Preferably Z is —COO—, —OCO—,—CH₂CH₂—, —C≡C— or a single bond, especially preferred is a single bond.

Very preferably the mesogenic groups MG¹¹ and MG¹², MG²¹ and MG²² andMG³¹ and MG³² are each and independently selected from the followingformulae and their mirror images

Very preferably at least one of the respective pairs of mesogenic groupsMG¹¹ and MG¹², MG²¹ and MG²² and MG³¹ and MG³² is, and preferably bothof them are each and independently, selected from the following formulaeIIa to IIn (the two reference Nos. “II i” and “II I” being deliberatelyomitted to avoid any confusion) and their mirror images

whereinL is in each occurrence independently of each other F or Cl, preferablyF andr is in each occurrence independently of each other 0, 1, 2 or 3,preferably 0, 1 or 2.The group

in these preferred formulae is very preferably denoting

or

furthermore

Particularly preferred are the subformulae IIa, IId, IIg, IIh, IIi, IIkand IIo, in particular the subformulae IIa and IIg.

In case of compounds with an non-polar group, R¹¹ and R¹², R²¹ and R²²and R³¹ and R³² are preferably alkyl with up to 15 C atoms or alkoxywith 2 to 15 C atoms.

If R¹¹ and R¹², R²¹ and R²² and R³¹ and R³² are an alkyl or alkoxyradical, i.e. where the terminal CH₂ group is replaced by —O—, this maybe straight-chain or branched. It is preferably straight-chain, has 2,3, 4, 5, 6, 7 or 8 carbon atoms and accordingly is preferably ethyl,propyl, butyl, pentyl, hexyl, heptyl, octyl, ethoxy, propoxy, butoxy,pentoxy, hexoxy, heptoxy, or octoxy, furthermore methyl, nonyl, decyl,undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, nonoxy, decoxy,undecoxy, dodecoxy, tridecoxy or tetradecoxy, for example.

Oxaalkyl, i.e. where one CH₂ group is replaced by —O—, is preferablystraight-chain 2-oxapropyl (=methoxymethyl), 2- (=ethoxymethyl) or3-oxabutyl (=2-methoxyethyl), 2-, 3-, or 4-oxapentyl, 2-, 3-, 4-, or5-oxahexyl, 2-, 3-, 4-, 5-, or 6-oxaheptyl, 2-, 3-, 4-, 5-, 6- or7-oxaoctyl, 2-, 3-, 4-, 5-, 6-, 7- or 8-oxanonyl or 2-, 3-, 4-, 5-, 6-,7-, 8- or 9-oxadecyl, for example.

In case of a compounds with a terminal polar group, R¹¹ and R¹², R²¹ andR²² and R³¹ and R³² are selected from CN, NO₂, halogen, OCH₃, OCN, SCN,COR^(x), COOR^(x) or a mono-oligo- or polyfluorinated alkyl or alkoxygroup with 1 to 4 C atoms. R^(x) is optionally fluorinated alkyl with 1to 4, preferably 1 to 3 C atoms. Halogen is preferably F or Cl.

Especially preferably R¹¹ and R¹², R²¹ and R²² and R³¹ and R³² informulae A-I, A-II, respectively A-III are selected of H, F, Cl, CN,NO₂, OCH₃, COCH₃, COC₂H₅, COOCH₃, COOC₂H₅, CF₃, C₂F₅, OCF₃, OCHF₂, andOC₂F₅, in particular of H, F, Cl, CN, OCH₃ and OCF₃, especially of H, F,CN and OCF₃.

In addition, compounds of formulae A-I, A-II, respectively A-IIIcontaining an achiral branched group R¹¹ and/or R²¹ and/or R³¹ mayoccasionally be of importance, for example, due to a reduction in thetendency towards crystallization. Branched groups of this type generallydo not contain more than one chain branch. Preferred achiral branchedgroups are isopropyl, isobutyl (=methylpropyl), isopentyl(=3-methylbutyl), isopropoxy, 2-methyl-propoxy and 3-methylbutoxy.

The spacer groups Sp¹, Sp² and Sp³ are preferably a linear or branchedalkylene group having 5 to 40 C atoms, in particular 5 to 25 C atoms,very preferably 5 to 15 C atoms, in which, in addition, one or morenon-adjacent and non-terminal CH₂ groups may be replaced by —O—, —S—,—NH—, —N(CH₃)—, —CO—, —O—CO—, —S—CO—, —O—COO—, —CO—S—, —CO—O—,—CH(halogen)-, —CH(CN)—, —CH═CH— or —C≡C—.

“Terminal” CH₂ groups are those directly bonded to the mesogenic groups.Accordingly, “non-terminal” CH₂ groups are not directly bonded to themesogenic groups R¹¹ and R¹², R²¹ and R²² and R³¹ and R³².

Typical spacer groups are for example —(CH₂)_(o)—,—(CH₂CH₂O)_(p)—CH₂CH₂—, with o being an integer from 5 to 40, inparticular from 5 to 25, very preferably from 5 to 15, and p being aninteger from 1 to 8, in particular 1, 2, 3 or 4.

Preferred spacer groups are pentylene, hexylene, heptylene, octylene,nonylene, decylene, undecylene, dodecylene, octadecylene,diethyleneoxyethylene, dimethyleneoxybutylene, pentenylene, heptenylene,nonenylene and undecenylene, for example.

Especially preferred are compounds of formulae A-I, A-II and A-IIIwherein Sp¹, Sp², respectively Sp³ are alkylene with 5 to 15 C atoms.Straight-chain alkylene groups are especially preferred.

Preferred are spacer groups with even numbers of a straight-chainalkylene having 6, 8, 10, 12 and 14 C atoms.

In another embodiment of the present invention are the spacer groupspreferably with odd numbers of a straight-chain alkylene having 5, 7, 9,11, 13 and 15 C atoms. Very preferred are straight-chain alkylenespacers having 5, 7, or 9 C atoms.

Especially preferred are compounds of formulae A-I, A-II and A-IIIwherein Sp¹, Sp², respectively Sp³ are completely deuterated alkylenewith 5 to 15 C atoms. Very preferred are deuterated straight-chainalkylene groups. Most preferred are partially deuterated straight-chainalkylene groups.

Preferred are compounds of formula A-I wherein the mesogenic groupsR¹¹-MG¹¹- and R¹²-MG¹- are different. Especially preferred are compoundsof formula A-I wherein R¹¹-MG¹¹- and R¹²-MG¹²- in formula A-I areidentical.

Preferred compounds of formula A-I are selected from the group ofcompounds of formulae A-I-1 to A-I-3

wherein the parameter n has the meaning given above and preferably is 3,5, 7 or 9, more preferably 5, 7 or 9.

Preferred compounds of formula A-II are selected from the group ofcompounds of formulae A-II-1 to A-II-4

wherein the parameter n has the meaning given above and preferably is 3,5, 7 or 9, more preferably 5, 7 or 9.

Preferred compounds of formula A-III are selected from the group ofcompounds of formulae A-III-1 to A-III-11

wherein the parameter n has the meaning given above and preferably is 3,5, 7 or 9, more preferably 5, 7 or 9.

Particularly preferred exemplary compounds of formulae A-I are thefollowing compounds:

symmetrical ones:

and non-symmetrical ones:

Particularly preferred exemplary compounds of formulae A-II are thefollowing compounds:

symmetrical ones:

and non-symmetrical ones:

Particularly preferred exemplary compounds of formulae A-III are thefollowing compounds:

symmetrical ones:

and non-symmetrical ones:

The compounds of formulae B-I to B-III are either known to the expertand can be synthesized according to or in analogy to methods which areknown per se and which are described in standard works of organicchemistry such as, for example, Houben-Weyl, Methoden der organischenChemie, Thieme-Verlag, Stuttgart.

The compounds of formulae A-I to A-III can be synthesized according toor in analogy to methods which are known per se and which are describedin standard works of organic chemistry such as, for example,Houben-Weyl, Methoden der organischen Chemie, Thieme-Verlag, Stuttgart.A preferred method of preparation can be taken from the followingsynthesis scheme.

The bimesogenic compounds of formulae A-I to A-III are either known tothe expert, can be prepared by known methods analogously to knowncompounds or are prepared according to the following general reactionschemes.

wherein R independently in each appearance has the meaning given for R¹¹and R¹² including the preferred meanings of these groups, mostpreferably is F or CN, and the conditions of the successive reactionsare as follows:

a) CuI, Pd(PPh₃)₂Cl₂, Triethylamine, 30° C.; b) [H₂], Pd/C;

c) n-BuLi, CO₂, −70° C.;

d) DCC, DMAP, DCM, 25° C.; and

e) Pd(PPh₃)₂Cl₂, NaCO3, THF, under reflux.

All phenylene moieties shown in this scheme and in the following schemesmay independently of each other be optionally bearing one, two or three,preferably one or two, F atoms or one Cl atom or one Cl and one F atom.

An exemplary reaction scheme for the preparation of such a fluorinatedcompound is shown in the following scheme.

wherein R independently in each appearance has the meaning given underscheme I and the conditions of the successive reactions are also asgiven under scheme I.

wherein R independently in each appearance has the meaning given for R¹¹and R¹² including the preferred meanings of these groups, mostpreferably is F or CN, and the conditions of the successive reactionsare as follows:a) benzylbromide, K₂CO₃, butanone, 80° C.;

b) CuI, Pd(PPh₃)₂Cl₂, Triethylamine, 30° C.; c) [H₂], Pd/C; and

d) K₂CO₃, butanone, 80° C.

wherein the conditions of the successive reactions are as given underscheme III. Steps d) and e) are performed under the same conditions.

wherein R independently in each appearance has the meaning given for R¹¹and R¹² including the preferred meanings of these groups, mostpreferably is F or CN, and the conditions of the successive reactionsare as follows:

a) CuI, Pd(PPh₃)₂Cl₂, Triethylamine, 30° C.; b) [H₂], Pd/C;

c) n-BuLi, THF, −70 0° C., CO₂;

d) HSC₃H₆SH, CF₃SO₃H, 130° C.; and e) N(C₂H₅)₃, 3HF.N(C₂H₅)₃, −70° C.

wherein the conditions of the successive reactions are as follows:

a) (i) HBr, 0° C.; (ii) H₂O₂, 0° C.; b) DCC, DMAP, DCM;

c1) AlCl₃, S(CH₃)₂, DCM, 0° C.;c2) K₂CO₃, butanone, 80° C.; andd) K₂CO₃, butanone, 80° C.

The compounds of formula A-II can be synthesized preferably by themethod shown in following synthesis scheme, reaction scheme VII.

a) K₂CO₃, THF, H₂O, Pd catalyst, 80° C., 24 hoursb) THF, Et₃N, CuI, Pd catalyst, 40° C., 24 hours

c) THF, Pd/C, H₂, 60° C., 95 bar

d) n-BuLi, THF, I₂. −70° C.e) Na₂CO₃, THF, H₂O, Pd catalyst, 80° C., 24 hourswherein R independently in each occurrence has the meaning of R¹¹ andR¹², o, o L and r are at each occurrence independently from each otheras defined above, including the preferred meanings of these groups.

COMPOUND AND SYNTHESIS EXAMPLES Synthesis Example 1 Preparation ofN-PGIZIGI-9-GZGP-N

Step 1.1

55.1 g (183 mmol) of the iodobromofluorobenzene and 60 mltetrahydrofuran are added to a reaction flask, which is evacuated threetimes and subsequently filled with nitrogen, then treated in anultrasonic bath to degas the reaction mixture, a procedure shortlyreferred to as “ultasonication” in this application, for 10 min. withadditional evacuation/purging with nitrogen. Pd(PPh₃)₂Cl₂ (1.8 g, 2.6mmol) and CuI (0.4 g, 2.1 mmol) as catalysts and diisopropylamine (60ml) are added and the reaction vessel is purged again before being“ultrasonicated” for 10 minutes and then placed in a large water bath tocontrol the reaction temperature.

1,8-nonadiyne (10 g, 83 mmol) are added slowly over a time span of 15minutes a fine precipitate is formed. The reaction mixture is stirredovernight at ambient temperature.

The reaction mixture is then filtered under vacuum and the filter padwashed with Dichloromethane. The filtrate is concentrated to asemi-solid, which is re-dissolved in dichloromethane before being passedthrough a silica column to purify. The target product is eluted withadditional dichloromethane before final isolation by re-crystallisationfrom petroleum ether.

Step 1.2

The hydrogenation reaction is performed in an “H-Cube”-hydrogenationapparatus. The parameters of the reaction are as follows: Flow rate: 7ml/min, Mode: 100% H₂, Catalysts: Pt/C, Temperature: 50° C. andPressure: 30 bar.

Step 1.3

Anhydrous tetrahydrofuran is charged into a three neck flask togetherwith 9.4 g (19.8 mmol) of the dibromide with the saturated spacer. Theflask is evacuated and filled with nitrogen. The reaction mixture isstirred and cooled to a temperature of −75° C. in a bath of acetonecooled by solid CO₂.

Then 31 ml 1.6 M, (49.5 mmol) n-butyl lithium are added drop wise over atime span of 30 minutes while keeping the temperature at −75° C. After 3hours further stirring 8.7 g (200 mmol) of crushed, solid CO₂ arecautiously added to the reaction mixture. A thick white sludge developsand this is stirred for a further 30 minutes before it is hydrolysed bythe addition of dilute HCl. The mixture is extracted three times withdiethyl ether, and the combined organic material washed with water untilneutral. Then toluene is added and the whole solvent is solution isevaporated. The solid the product is isolated and used in the followingwithout further purification.

Step 1.4

4.9 g (24 mmol) of the acid intermediate are added to flask filled with50 ml dichloromethane. This mixture is thoroughly stirred before 6.5 g(31 mmol) of trifluoroacetic anhydride are added dropwise over a timespan of 5 minutes. The reaction mixture is then stirred further for 5minutes.

Then 4.6 g (24.4 mmol) of solid 4-hydroxy-3-fluorobromobenzene are addedand the reaction mixture is stirred at a temperature of 35° C. Aftercomplete reaction, water is added. The organic and aqueous layers areseparated and the aqueous solution is extracted three times withdichloromethane. The combined organic solutions are washed with asolution of sodium carbonate before being dried over magnesium sulphate,filtered and concentrated. The crude product is purified by passingthrough a silica plug and eluting with a mixture of petrol anddichloromethane (1:2). The final purification is carried out byre-crystallisation from MeCN.

Step 1.5

1.0 g (1.33 mmol) of the bromide intermediate, 0.61 g (2.67 mmol) of4-cyanophenyl boronate ester, 0.63 g (2.66 mmol) of sodium metaborateoctahydrate, 9.0 ml (499 mmol) of water and 37.5 ml (463 mmol) oftetrahydrofuran are filled into a round bottom flask. This mixture isstirred, the flask is evacuated and filled with nitrogen before being“untrasonicated” for 30 minutes. Then 0.075 g (0.107 mmol) of palladiumdichloride-(bistriphenylphosphine) are added and the vessel is evacuatedthen filled with nitrogen. The reaction mixture is heated to atemperature of 80° C. for 72 hours under reflux. Then the reactionmixture is cooled, water and diethyl ether are added subsequently. Thenthe resulting phases are separated. The aqueous phase is extracted twicewith diethyl ether, and the combined organic phases are washed twicewith water and once with an aqueous solution of NaCl. The organicsolution is dried over sodium sulphate, filtered and the solventevaporated. The crude product is purified over a short silica column,eluted with first petrol then with a mixture of petrol/dichloromethane(2:1). The product is isolated after repeated re-crystallisation fromacetonitrile.

This compound has the phase sequence: K 130 Sm 255 N 271 I.

Scheme for Synthesis Example 2—Preparation of N-PO1GI-9-GO1P-N

Synthesis Example 2 Step 2.1

4-bromofluorophenol (33.9 g, 0.178 moles), benzylbromide (21.1 ml, 0.178moles), potassium carbonate (34.4 g, 0.25 moles) and butan-2-one (300ml) are heated together at a temperature of 85° C. under refluxovernight. The mixture is cooled, filtered, washed with butanone anddiethyl ether and the solvent removed in vacuo. The material isre-crystallised from heptane at −20° C.

Step 2.2

The bromide (44.5 g, 115.8 mmol) from the previous step, triethylamine(89 ml), tetrahydrofuran (45 ml), Copper(I) Iodide (0.694 g, 3.6 mmol)and bis(triphenylphosphine)Palladium(II)dichloride (3.5 g, 4.91 mmol)are added to a flask and then 1,8-Nonadiyne (9.14 g (76.0 mmol) intetrahydrofuran (45 ml) is slowly added over a time of 30 minutes. Thereaction-mixture is warmed to 40° C. overnight. The mixture is thencooled, filtered and the filter pad washed with diethyl ether. Thefiltrate is acidified with dilute Hydrochloric acid and then neutralizedwith sodium hydroxide before drying over sodium sulphate. This wasfiltered and the solvent from the filtrate removed in vacuo to give asolid product. The solid was pre-adsorbed onto 50 g silica from adichloromethane solution and columned through a short silica columnusing 10% DCM in petrol as eluent. The fractions containing the productwere collected and re-crystallised first from petrol and then fromacetonitrile to afford the clean product.

Step 2.3

The hydrogenation reaction is again performed in a an “H-Cube”Hydrogenator.

Parameters: Flow: 10 ml/min., Mode: 100% H₂ Catalysts: Pd/C

Temp.: 50° C., Pressure: 30 bar Rising to 80 CC and 80 bar at the end ofthe reaction.

Stage 2.4

The phenol from stage 3 (2.80 g, 8.04 mmol), 4-bromomethylbenzonitrile(3.94 g, 20.09 mmol) and potassium carbonate (1.66 g, 12 mmol) are addedto a flask with dimethylformamide (5.87 g) and ethyl methyl ketone (50ml). The mixture is heated at 85° C. overnight. The mixture is cooled,filtered and the filter pad washed with diethyl ether and the solventfrom the filtrate removed in vacuo to give a solid product. This solidcrude product is purified over a short silica column using 33% DCM inpetrol as eluent. The fractions containing the product are collected andre-crystallised from acetonitrile to afford the clean product.

Scheme for Synthesis Example 3—Preparation of N-PO1GI-9-GO1P-F

Synthesis Example 3

Steps 3.1 to 3.3 are identical to those of Synthesis example 2.

Step 3.4

The product of the synthesis example 2, step 2.3 (2.50 g, 7.18 mmol),4-bromomethyl-benzonitrile (2.81 g, 14.4 mmol) and potassium carbonate(1.79 g, 19.9 mmol) are mixed together in ethylmethylketone (50 ml). Thereaction mixture is heated under reflux at 80° C. for 12 hours. Thereaction-mixture is then cooled and the solid precipitate formed isfiltered off under vacuum, the filter pad is washed with ether then thesolution is concentrated under reduced pressure. The crude product ispurified by chromatography through silica, eluted with 30% DCM inpetroleum ether (40-60). The material is then re-crystallised fromacetonitrile to yield the desired non symmetrical intermediate alcohol.

Step 3.5

The product from the previous step, step 3.4 (2.15 g, 4.64 mmol),1-bromomethyl-4-fluorobenzene (1.05 g, 5.56 mmol) and potassiumcarbonate (1.92 g, 14.0 mmol) are mixed together in ethylmethylketone(50 ml). The reaction mixture is heated under reflux at 80° C. for 18hours. The reaction-mixture is then cooled and solids filtered off undervacuum, the filter pad is washed with diethyl ether then concentratedunder reduced pressure. The crude product is purified by chromatographythrough silica, eluted with 30% DCM in petroleum ether (40-60). Thematerial was then re-crystallised twice from acetonitrile to afford theproduct.

Scheme for Synthesis Example 4-Preparation of N-PQIP-9-PQP-N

Step 4.1

25.0 g (88.4 mmol) of iodobromobenzene and 80 ml tetrahydrofuran areadded to a reaction flask, which is evacuated three times andsubsequently filled with nitrogen each time, then “ultasonicated” for 10min. with additional evacuation/purging with nitrogen. Pd(PPh₃)₂Cl₂ (0.9g, 1.3 mmol) and CuI (0.2 g, 1.1 mmol) as catalysts and diisopropylamine(14 ml) are added and the reaction vessel is purged again before beingplaced back in an ultrasonic bath for 10 minutes and then placed in alarge water bath to control the reaction temperature.

1,8-nonadiyne (5.0 g, 41.6 mmol) is mixed with tetrahydrofuran (20 ml)and added slowly over a time span of 15 minutes. A fine precipitate isformed. The reaction mixture is stirred overnight at ambienttemperature. The reaction mixture is then filtered under vacuum and thefilter pad washed with tetrahydrofuran. The filtrate is concentrated toa semi-solid, which is re-dissolved in dichloromethane before beingpassed through a silica column for purification. The target product iseluted with additional dichloromethane to afford a yellow crystallinesolid.

Step 4.2

The hydrogenation reaction is performed in an “H-Cube”-hydrogenationapparatus. The parameters of the reaction are as follows: Flow rate: 7ml/min., Mode: 100% H₂, Catalysts: Pt/C, Temperature: 50° C., andPressure: 30 bar.

Step 4.3

Anhydrous tetrahydrofuran is charged into a three neck flask togetherwith 9.4 g (19.8 mmol) of the dibromide from the previous stage. Theflask is evacuated and filled with nitrogen. The reaction mixture isstirred and cooled to a temperature of −75° C. in a bath of acetonecooled by solid CO₂.

Then n-butyl lithium (1.6 M, 31 ml, 49.5 mmol) are added drop wise overa time span of 30 minutes while keeping the temperature at −75° C. After3 hours further stirring 8.7 g (200 mmol) of crushed, solid CO₂ arecautiously added to the reaction mixture. A thick white sludge developsand this is stirred for a further 30 minutes before it is hydrolysed bythe addition of dilute HCl. The mixture is extracted three times withdiethyl ether, and the combined organic material washed with water untilneutral. Then toluene is added and the whole solvent is solution isevaporated. The solid the product is isolated and used in the followingwithout further purification.

Step 4.4

The intermediate product from the previous stage (5.5 g, 15 mmol) andpropandithiol (3.6 g, 33 mmol) are added to flask before addingtrifluoromethanesulphonic acid (6.8 g, 45 mmol) and starting to stir themixture. The mixture is heated to 120° C. and the now clear orangemixture is then cooled to ambient before being treated with diethylether (300 ml). The resultant solution is added to a flask of vigorouslystirred diethyl ether (700 ml) pre-cooled to −70° C. Within 30 minutesfine crystals appear in the stirred mixture. The solid is isolated byfiltration under vacuum and washed with ether to give a pale yellowpowder which is used immediately.

Step 4.5

The intermediate (10.1 g 12 mmol) from the previous stage is added to aflask with dichloromethane (50 ml) and then cooled to −70° C. A mixtureof 4-cyanophenol (3.5 g, 30 mmol), dichloromethane (40 ml) andtriethylamine (3.5 g, 34 mmol) is added dropwise. After 90 minutesfurther stirring triethylaminehydrogen fluoride (20 g, 125 mmol) isadded dropwise. After a further hour of stirring bromine (19.9 g, 125mmol) in dichloromethane (100 ml) is added dropwise. The reactionmixture is stirred for 30 minutes and allowed to warm to −30° C. beforeadding morpholine (10.9 g, 125 mmol) and finally warming to 0° C. whereit is stirred for a further time span of 1 hour. The mixture iscarefully poured onto a mixture of ice, water and potassium hydroxide,and the layers are separated. The organic material is washed with water,dried over sodium sulphate and concentrated in vacuo. The crude materialis purified by flash chromatography, eluting with a solution of 30% DCMin petroleum ether. Final purification is carried out by repeatedre-crystallisation from acetonitrile to afford the desired product.

Scheme for Synthesis Example 5—Preparation of N-PQIG-9-GQP-N

Steps 5.1 to 5.3 are identical to the respective steps of SynthesisExample 1.

Step 5.4

The intermediate product of Synthesis Example 1, step 1.3 (5.5 g, 15mmol) and propandithiol (3.6 g, 33 mmol) are added to flask beforeadding trifluoromethanesulphonic acid (6.8 g, 45 mmol) and starting tostir the mixture. The mixture is heated to 120° C. and the then clearorange mixture is cooled to ambient before being treated with diethylether (300 ml). The resultant solution is added to a flask of vigorouslystirred diethyl ether (700 ml) pre-cooled to −70° C. Within 30 minutesfine crystals appear in the stirred mixture. The solid is isolated byfiltration under vacuum and washed with ether to give a pale yellowpowder which is used immediately.

Step 5.5

The intermediate (10.1 g 12 mmol) from the previous step is added to aflask with dichloromethane (50 ml) and then cooled to −70° C. A mixtureof 4-cyanophenol (3.5 g, 30 mmol), dichloromethane (40 ml) andtriethylamine (3.5 g, 34 mmol) is added dropwise. After 90 minutesfurther stirring triethylaminehydrogen fluoride (20 g, 125 mmol) isadded dropwise. After a further hour of stirring bromine (19.9 g, 125mmol) in dichloromethane (100 ml) is added dropwise. The reactionmixture is stirred for 30 minutes and allowed to warm to −30° C. beforeadding morpholine (10.9 g, 125 mmol) and finally warming to 0° C. whereit is stirred for a further time span of 1 hour. The mixture iscarefully poured onto a mixture of ice, water and potassium hydroxide,and the layers are separated. The organic material is washed with water,dried over sodium sulphate and concentrated in vacuo. The crude materialis purified by flash chromatography, eluting with a solution of 30% DCMin petroleum ether. Final purification is carried out by repeatedre-crystallisation from acetonitrile to afford the desired product.

Scheme for Synthesis Example 6—Preparation of Chiral

Step 6.1

Methylbutylbiphenyl (44.8 g, 0.2 mol), dichloromethane (250 ml),tetraethyl-ammonium bromide (2.1 g, 10 mmol) and hydrogen bromide (51.6g, 0.3 mol) are introduced into a reaction flask and cooled to 0° C.Hydrogen peroxide (48.6 g, 0.5 mol) is added with a dosage of 0.1ml/min.

After the reaction is shown to have completed (by TLC analysis), thereaction is cooled to 0-10° C. and sodium sulfite (17.8 g, 014 mol) asan aqueous solution is added until de-coloration occurs. Thereby, thetemperature is maintained at 10° C. The solution turns green. Then thereaction mixture is stirred for 2 hours. Subsequently a 10% sodiumcarbonate solution is prepared and added. The resultant two phases areseparated. The aqueous phase is extracted with 100 ml of dichloromethaneand added to the organic phase.

The material is washed with sodium carbonate solution and then waterbefore being concentrated in vacuo.

The residue is then dissolved in 150 ml ethanol and heated for 3 hoursunder reflux.

The solution is drained and cooled in an ice bath. The resultingcrystals are filtered off and dried under ambient atmosphere.

Step 6.2

To a stirred solution of the cyano biphenol (25.0 g, 128 mmol) inacetone (625 ml), potassium carbonate (37.5 g, 271 mmol) is added,heated under reflux for 1 hour under a nitrogen atmosphere, and thencooled to ambient temperature. Dibromononane (200 ml, 961 mmol) is thenadded in a single portion. The reaction mixture is heated again toreflux. After heating under reflux overnight the reaction was cooled andfiltered under vacuum, the filter pad washed with dcm, and the filtrateevaporated under reduced pressure to afford the crude material. This wasvacuum distilled on Kugelrohr apparatus to remove excess dibromononaneaffording a solid pale yellow product.

Step 6.3

4-methoxybenzoic acid (10 g, 65.7 mmol), intermediate from step 6.1(15.7 g, 65.3 mmol), Dicyclohexylcarbodiimide (13.5 g, 65.4 mmol),Dimethylamino pyridine (0.5 g) and Dichloromethane (250 ml) are added toa flask under nitrogen atmosphere stirred at 30° C. overnight. Theprogress of the reaction procedure is monitored by TLC. When thereaction appears complete, Oxalic acid (5.9 g, 65.7 mmol) is added, thenthe reaction mixture is filtered using vacuum and the filtrateevaporated to dryness in vacuo. The product is isolated as a whitesolid.

Step 6.4

The ester from step 6.3 (20 g, 53.4 mmol) is dissolved inDichloromethane (80 ml) and added to a suspension of aluminium chloride(35 g, 262 mmol) in Dichloromethane (80 ml) at a temperature in therange from 0° C. to −5° C. Dimethyl sulphide (21 ml, 284 mmol)) is thenadded dropwise, while the temperature is maintained below 0° C. and theresulting mixture (brown solution) is stirred overnight.

The reaction is quenched by the addition (which is exothermic) of(saturated) ammonium chloride solution until the resultant mixture isacidic leading to a white solid precipitate, diluted withDichloromethane and filtered off under vacuum collecting theprecipitate.

Step 6.5

The intermediate from Step 6.4 (3.5 g, 9.71 mmol), the intermediate fromstep 5.2 (4.0 g, 9.9 mmol), potassium iodide (1.8 g, 10.9 mmol),potassium carbonate (0.9 g, 6.5 mmol) and dimethylformamide (100 ml) areadded to a flask and heated at 100° C. under reflux for 48 hours.

The reaction is cooled, the reaction mixture poured into a mixture ofdichloromethane and water, the layers are separated and the organicsolution is washed with water, the organics are dried over sodiumsulphate, filtered and concentrated in vacuo to yield a yellow solid.

The material is purified by column chromatography, eluting with DCM withincreasing amounts of Industrial methylated spirits. The product isre-crystallized from acetone to give the final material.

Phase sequence: to be determined.

Compound Examples 7 to 24

The following compounds of formula I are prepared analogously.

Phase sequence: K 108.7 (N₂ 60 N 86) I.

Phase sequence: K 118.6 N 135.8 I.

Phase sequence: K 85.1.

Phase sequence: K 69.9 I.

Phase sequence: K 109.81 I.

Phase sequence: K 77.5 I.

The materials in the above table generally showed increased performancein the screening mixtures, as compared to known, rather conventionalbimesogenic compounds.

Example 25 General Synthesis Scheme for Compounds of Formula A-IIWherein R²¹-MG²¹- and R²²-MG²²- in Formula A-II are Identical to EachOther

Step 25.1: Synthesis of (1)

1-bromo-3-fluoroiodobenzene (53.3 g, 0.177 mol) is added to a roundbottom flask with 3,5-difluorobenzenboronic acid (29.0 g, 0.184 mol).Tetrahydrofuran (500 ml) is added and the mixture is stirred undernitrogen until dissolved. A solution of potassium carbonate (36.7 g,0.265 mol) in water (100 ml) is added to the reaction. A catalyst,bis(triphenylphosphine)-palladium(II) dichloride (1.98 g, 2.83 mmol) isadded and the reaction is heated to reflux for 18 hours. The reaction iscooled and diluted with water before being acidified with diluteHydrochloric acid. The layers are separated and the organics are washedwith water before being concentrated to obtain the product as a brownsolid.

The crude solid is dissolved in Dichloromethane and adsorbed onto silicagel (100 g) by concentration. The material is purified by columnchromatography, eluting with a mixture of petroleum spirit (40-60° C.)and dichloromethane to obtain a purified product as a yellow solid.

Step 25.2: Synthesis of (2)

2,-3′-5′-trifluoro-4-bromobiphenyl (26.1 g, 0.091 mol) is added to around bottomed flask. Triethylamine (25.0 ml) and tetrahydrofuran (50.0ml) is added and the whole evacuated and replaced with nitrogen.Copper(I)iodide (0.404 g, 2.12 mmol) andbis(triphenylphosphine)-palladium(II) dichloride (0.71 g, 1.01 mmol) areadded, the reaction is evacuated and replaced with nitrogen. Thereaction mixture is heated to 40° C. and 1,8-nonadiyne (5.25 g, 0.044mol) is slowly added over 30 minutes. The mixture is heated for afurther 24 hours at 40° C. followed by 48 hours at 80° C.

The reaction mixture is cooled and filtered under vacuum to removeprecipitates. The filtrate is acidified with dilute Hydrochloric acidand extracted with diethyl ether. The organic material is washed withwater before concentrating to afford the product as a black solid (26.0g). The crude solid is dissolved in dichloromethane and adsorbed onto50.0 g silica gel. The material is purified by column chromatography,eluting the product using a mixture of dichloromethane in petrol.

Step 25.3: Synthesis of (3)

The material (2) (21.5 g, 0.040 mol) is dissolved in Tetrahydrofuran(600 ml) and passed through a Thales nano hydrogenator. The materialrequired conditions of 70 bar pressure and 60° C. to produce the productas pale colored solid.

Step 25.4: Synthesis of (4)

Material (3) (21.5 g, 0.04 mol) is added to a round bottom flask withTetrahydrofuran (150 ml). The reaction is stirred under nitrogen andcooled to −70° C. n-Butyl Lithium solution (1.6 M in hexanes, 55.0 ml,0.087 mol) is slowly added over 45 minutes, and the reaction stirred fora further hour at −70° C. A solution of Iodine (45.8 g, 00.179 mol) intetrahydrofuran (125 ml) is slowly added keeping the temperature between−60 and −70° C. The reaction is stirred overnight and allowed to warm toroom temperature. The reaction is quenched by slowly adding wet THFbefore water and then ethyl acetate is added. The layers are separatedand the aqueous extracted three times with ethyl acetate. The organicsare washed twice with sodium thiosulphate solution (100 ml, 2 M inwater) then washed with water. Concentration afforded a brown solid. Thematerial is purified by sequential recrystallisations from Industrialmethylated spirits, acetone and acetonitrile/acetone.

Step 25.5: Synthesis of (5)

4-bromo-2-fluorobenzonitrile (42.4 g, 212 mmol) is added to a roundbottom flask along with bis(pinacolato)diborane (59.8 g, 235 mmol).Potassium acetate (31.1 g, 317 mmol), tricyclohexylphosphine (3.57 g,12.7 mmol), Tris(dibenzylideneacetone)dipalladium(0) (3.66 g, 6.36 mmol)and 1,4-dioxane (600 ml) are all added to the reaction flask and themixture stirred under nitrogen at 80° C. for 72 hours. After cooling thereaction mixture, water and diethyl ether are added and the layersseparated. The organic material is washed with brine and water beforeconcentrating to a brown solid. The product is purified byrecrystallisation from petrol/dichloromethane to obtain a browncrystalline solid.

Step 25.6: Synthesis of (6)

Material (4) (10.17 g, 12.8 mmol) and material (5) (7.70 g, 31.2 mmol)are added to a round bottom flask and dissolved in Tetrahydrofuran (250ml). Bis(triphenylphosphine)-palladium(II) dichloride (450.6 mg, 0.642mmol) is added along with a solution of sodium carbonate (1 M in water,77.0 ml, 77.0 mmol). The reaction is heated to 85° C. for 24 hours,after which it is cooled and diluted with water before being acidifiedwith dilute Hydrochloric acid. The layers are separated and the organiclayer is washed with water before being concentrated to yield theproduct as a brown solid. The material is purified by columnchromatography, eluting the product with 40% ethyl acetate in petrol.The product is further purified by recrystallisation from, first,acetone/methanol, then acetone and finally IPA/petrol.

Example 26 to 42

The following compounds of formula A-II are prepared analogously:

Phase sequence: K 84.1 SmC 105.7 N 122 I.

Phase sequence: to be determined.

Example 43 General Synthesis for Compounds of Formula A-II WhereinR²¹-MG²¹- and R²²-MG²²- in Formula A-II are Different from One Another

Step 43.1: Synthesis of (1)

1-bromo-3-fluoroiodobenzene (27.5 g, 92 mmol) is added to a round bottomflask with tetrahydrofuran (30 ml) and the mixture is stirred undernitrogen until dissolved. Diisopropylamine (30 ml) is added and thereaction placed in an ultrasonic bath for 10 minutes. Catalysts,bis(triphenyl-phosphine)palladium(II) dichloride (0.9 g, 1.28 mmol) andcopper(I)iodide (0.2 g, 1.05 mmol) are added and the reaction is cooledin a water bath to 20° C. 1,8-nonadiyne (5.0 g, 41 mmol) is slowly addedto the reaction and stirred for a further 20 hours. The reaction iscooled and filtered under vacuum to remove precipitates. The filtrate isacidified with diluted hydrochloric acid and extracted with diethylether. The organic material is washed with water before concentrating toafford the product as a black solid (19 g). The material is purified bycolumn chromatography, eluting the product using a mixture ofdichloromethane in petrol. This produces the desired product.

Step 43.2: Synthesis of (2)

Material (1) (21.5 g, 40 mmol) is dissolved in tetrahydrofuran (600 ml)and passed through a Thales nano hydrogenator. The material requiredconditions of 70 bar pressure and 60° C. to produce the product as palecoloured solid.

Step 43.3: Synthesis of (3)

Material (2) (14.35 g, 30.3 mmol), 4-cyanophenylboronic acid (4.45 g,30.3 mmol), potassium phosphate (25.4 g, 120 mmol), dioxane (57.4 ml)and water (28.7 ml) are sonicated in an ultrasound bath for 30 minutesunder a nitrogen atmosphere. The mixture is stirred at room temperatureand Pd(DPPF)Cl₂-DCM complex (215 mg) are added. The mixture is heated to90° C. for 2 hours. The mixture is cooled. The two layers are separatedand the solvent from the organic layer removed in vacuo to give a blackoil. This is dissolved in a minimum of DCM and applied to a column ofsilica eluting with petrol: DCM, 1:1 to give the desired product.

Step 43.4: Synthesis of (4)

Material (3) (3.5 g, 7.05 mmol), 3,4-difluorobenzeneboronic acid (1.7 g,8 mmol) potassium phosphate (1.7 g, 8 mmol), dioxane (10.6 ml) and water(5.3 ml) are sonicated in an ultrasound bath for 30 minutes under anitrogen atmosphere. The mixture is stirred at room temperature andPd(DPPF)Cl₂-DCM complex (59 mg) are added. The mixture is heated to 90°C. for 5 hours. The two layers are separated and the solvent from theorganic layer removed in vacuo. This is dissolved in a minimum of DCMand applied to a column of silica, eluting with petrol: DCM, 2:1. Thecrude product is crystallized twice from DCM/acetonitrile (cooled withdry ice/acetone bath) and the product is dissolved in a minimum of DCMand applied to a column of silica eluting with petrol: DCM, 2:1. Thecrude product is crystallized from acetonitrile (cooled with dryice/acetone bath) to give the desired product.

Another object of the invention is the use of bimesogenic compounds offormulae A-I and/or A-II and/or A-III in liquid crystalline media.

Compounds of formula A-II, when added to a nematic liquid crystallinemixture, producing a phase below the nematic. In this context, a firstindication of the influence of bimesogenic compounds on nematic liquidcrystal mixtures was reported by Barnes, P. J., Douglas, A. G., Heeks,S. K., Luckhurst, G. R., Liquid Crystals, 1993, Vol. 13, No. 4, 603-613.This reference exemplifies highly polar alkyl spacered dimers andperceives a phase below the nematic, concluding it is a type of smectic.

A photo evidence of an existing mesophase below the nematic phase waspublished by Henderson, P. A., Niemeyer, O., Imrie, C. T. in LiquidCrystals, 2001, Vol. 28, No. 3, 463-472, which was not furtherinvestigated.

In Liquid Crystals, 2005, Vol. 32, No. 11-12, 1499-1513 Henderson, P.A., Seddon, J. M. and Imrie, C. T. reported, that the new phase belowthe nematic belonged in some special examples to a smectic C phase. Aadditional nematic phase below the first nematic was reported by Panov,V. P., Ngaraj, M., Vij, J. K., Panarin, Y. P., Kohlmeier, A., Tamba, M.G., Lewis, R. A. and Mehl, G. H. in Phys. Rev. Lett. 2010, 105,1678011-1678014.

In this context, liquid crystal mixtures comprising the new andinventive bimesogenic compounds of formulae A-I and/or A-II and/or A-IIIshow also a novel mesophase that is being assigned as a second nematicphase. This mesophase exists at a lower temperature than the originalnematic liquid crystalline phase and has been observed in the uniquemixture concepts presented by this application.

Accordingly, the bimesogenic compounds of formula A-II according to thepresent invention allow the second nematic phase to be induced innematic mixtures that do not have this phase normally. Furthermore,varying the amounts of compounds of formula A-II allow the phasebehaviour of the second nematic to be tailored to the requiredtemperature.

Some preferred embodiments of the mixtures according to the inventionare indicated below.

Preferred are compounds of formulae A-I and/or A-II and/or A-III whereinthe mesogenic groups MG¹¹ and MG¹², MG²¹ and MG²² and MG³¹ and MG³² ateach occurrence independently from each other comprise one, two or threesix-atomic rings, preferably two or three six-atomic rings.

Particularly preferred are the subformulae II-1, II-4, II-6, II-7,II-13, II-14, II-15, II-16, II-17 and II-18.

Especially preferred are the subformulae IIa, IId, IIg, IIh, IIi, IIkand IIo, in particular the subformulae IIa and IIg, wherein L is in eachoccurrence independently of each other preferably F, Cl, CN, OH, NO₂ oran optionally fluorinated alkyl, alkoxy or alkanoyl group with 1 to 7 Catoms, very preferably F, Cl, CN, OH, NO₂, CH₃, C₂H₅, OCH₃, OC₂H₅,COCH₃, COC₂H₅, COOCH₃, COOC₂H₅, CF₃, OCF₃, OCHF₂, 0C₂F₅, in particularF, Cl, CN, CH₃, C₂H₅, OCH₃, COCH₃ and OCF₃, most preferably F, Cl, CH₃,OCH₃ and COCH₃.

Preferably R¹¹ and R¹², R²¹ and R²² and R³¹ and R³² in formula I areselected of H, F, Cl, CN, NO₂, OCH₃, COCH₃, COC₂H₅, COOCH₃, COOC₂H₅,CF₃, C₂F₅, OCF₃, OCHF₂, and OC₂F₅, in particular of H, F, Cl, CN, OCH₃and OCF₃, especially of H, F, CN and OCF₃.

Typical spacer groups (Sp) are for example —(CH₂)_(o)—,—(CH₂CH₂O)_(p)—CH₂CH₂—, with o being an integer from 5 to 40, inparticular from 5 to 25, very preferably from 5 to 15, and p being aninteger from 1 to 8, in particular 1, 2, 3 or 4.

Especially media comprise one or more compounds of formula A-I whereinR¹¹-MG¹¹- and R¹²-MG¹²- are identical to each other.

In another preferred embodiment of the present invention the media mediacomprise one or more to compounds of formula A-I wherein R¹¹-MG¹¹- andR¹²-MG¹²- are different from one another.

Especially media comprise one or more compounds of formula A-II whereinR²¹-MG²¹- and R²²-MG²²- are identical to each other.

In another preferred embodiment of the present invention the media mediacomprise one or more to compounds of formula A-II wherein R²¹-MG²¹- andR²²-MG²²- are different from one another.

Especially media comprise one or more compounds of formula A-III whereinR³¹-MG³¹-X³¹— and R³²-MG³²-X³²— are identical to each other.

In another preferred embodiment of the present invention the mediacomprise one or more to compounds of formula A-III wherein R³¹-MG³¹-X³¹—and R³²-MG³²-X³²— are different from one another.

Especially preferred are compounds of formula A-III wherein themesogenic groups MG³¹ and MG³² comprise one, two or three six-atomicrings very preferably are the mesogenic groups selected from formula IIas listed below.

For MG³¹ and MG³² in formula A-III are particularly preferred are thesubformulae II-1, II-4, II-6, II-7, II-13, II-14, II-15, II-16, II-17and II-18. In these preferred groups Z in each case independently hasone of the meanings of Z¹ as given in formula II. Preferably Z is —COO—,—OCO—, —CH₂CH₂—, —C≡C— or a single bond.

Very preferably the mesogenic groups MG³¹ and MG³² are selected from theformulae IIa to IIo and their mirror images.

Particularly preferred for MG³¹ and MG²³ are the subformulae IId, IIg,IIh, IIi, IIk and IIo, in particular the subformulae IId and IIk.

In case of compounds with a non-polar group, R¹¹, R¹², R²¹, R²², R³¹ andR³² are preferably alkyl with up to 15 C atoms or alkoxy with 2 to 15 Catoms.

If In case of compounds with an non-polar group, R¹¹, R¹², R²¹, R²², R³¹or R³² is an alkyl or alkoxy radical, i.e. where the terminal CH₂ groupis replaced by —O—, this may be straight-chain or branched. It ispreferably straight-chain, has 2, 3, 4, 5, 6, 7 or 8 carbon atoms andaccordingly is preferably ethyl, propyl, butyl, pentyl, hexyl, heptyl,octyl, ethoxy, propoxy, butoxy, pentoxy, hexoxy, heptoxy, or octoxy,furthermore methyl, nonyl, decyl, undecyl, dodecyl, tridecyl,tetradecyl, pentadecyl, nonoxy, decoxy, undecoxy, dodecoxy, tridecoxy ortetradecoxy, for example.

Oxaalkyl, i.e. where one CH₂ group is replaced by —O—, is preferablystraight-chain 2-oxapropyl (=methoxymethyl), 2- (=ethoxymethyl) or3-oxabutyl (=2-methoxyethyl), 2-, 3-, or 4-oxapentyl, 2-, 3-, 4-, or5-oxahexyl, 2-, 3-, 4-, 5-, or 6-oxaheptyl, 2-, 3-, 4-, 5-, 6- or7-oxaoctyl, 2-, 3-, 4-, 5-, 6-, 7- or 8-oxanonyl or 2-, 3-, 4-, 5-, 6-,7-, 8- or 9-oxadecyl, for example.

Preferred spacer groups are pentylene, hexylene, heptylene, octylene,nonylene, decylene, undecylene, dodecylene, octadecylene,diethyleneoxyethylene, dimethyleneoxybutylene, pentenylene, heptenylene,nonenylene and undecenylene, for example.

Especially preferred are inventive compounds of formula A-I and A-II andA-III wherein Sp¹ respectively Sp², respectively Sp³ is denotingalkylene with 5 to 15 C atoms. Straight-chain alkylene groups areespecially preferred.

Particularly preferred media according to the invention comprise atleast one or more chiral dopants which themselves do not necessarilyhave to show a liquid crystalline phase and give good uniform alignmentthemselves.

The compounds of formula C-II and their synthesis are described in WO98/00428. Especially preferred is the compound CD-1, as shown in table Dbelow. The compounds of formula C-III and their synthesis are describedin GB 2 328 207.

Especially preferred are chiral dopants with a high helical twistingpower (HTP), in particular those disclosed in WO 98/00428.

Further typically used chiral dopants are e.g. the commerciallyavailable R/S-5011, CD-1, R/S-811 and CB-15 (from Merck KGaA, Darmstadt,Germany).

The above mentioned chiral compounds R/S-5011 and CD-1 and the (other)compounds of formulae C-I, C-II and C-III exhibit a very high helicaltwisting power (HTP), and are therefore particularly useful for thepurpose of the present invention.

The liquid crystalline medium preferably comprises preferably 1 to 5, inparticular 1 to 3, very preferably 1 or 2 chiral dopants, preferablyselected from the above formula C-II, in particular CD-1, and/or formulaC-III and/or R-5011 or S-5011, very preferably the chiral compound isR-5011, S-5011 or CD-1.

The amount of chiral compounds in the liquid crystalline medium ispreferably from 1 to 20%, in particular from 1 to 15%, very preferably 1to 10% by weight of the total mixture.

Further preferred are liquid crystalline media comprising in component Bone or more nematogens of formula B-I selected from the from the groupof formulae B-I-1 to B-I-, preferably of formula B-I-2 and/or B-I-4,most preferably B-I-4

wherein the parameters have the meanings given above and preferably

-   R^(B1) is alkyl, alkoxy, alkenyl or alkenyloxy with up to 12 C    atoms, and-   L^(B1) and L^(B1) are independently H or F, preferably one is H and    the other H or F and most preferably both are H.

Further preferred are liquid crystalline media comprising in component Bone or more nematogens of formula B-II selected from the from the groupof formulae B-II-1 and B-II-2, preferably of formula B-II-2 and/orB-II-4, most preferably of formula B-II-1

wherein the parameters have the meanings given above and preferably

-   R^(B21) and R^(B22) are independently alkyl, alkoxy, alkenyl or    alkenyloxy with up to 12 C atoms, more preferably R^(B21) is alkyl    and R^(B22) is alkyl, alkoxy or alkenyl and in formula B-II-1 most    preferably alkenyl, in particular vinyl or 1-propenyl, and in    formula B-II-2, most preferably alkyl.

Further preferred are liquid crystalline media comprising in component Bone or more nematogens of formula B-III, preferably of formula B-III-1

wherein the parameters have the meanings given above and preferably

-   R^(B31) and R^(B32) are independently alkyl, alkoxy, alkenyl or    alkenyloxy with up to 12 C atoms, more preferably R^(B31) is alkyl    and R^(B32) is alkyl or alkoxy and most preferably alkoxy, and-   L^(B31) and L^(B32) are independently H or F, preferably one is F    and the other H or F and most preferably both are F.

The liquid crystal media according to the present invention may containfurther additives in usual concentrations. The total concentration ofthese further constituents is in the range of 0.1% to 10%, preferably0.1% to 6%, based on the total mixture. The concentrations of theindividual compounds used each are preferably in the range of 0.1% to3%. The concentration of these and of similar additives is not takeninto consideration for the values and ranges of the concentrations ofthe liquid crystal components and compounds of the liquid crystal mediain this application. This also holds for the concentration of thedichroic dyes used in the mixtures, which are not counted when theconcentrations of the compounds respectively the components of the hostmedium are specified. The concentration of the respective additives isalways given relative to the final doped mixture.

The liquid crystal media according to the present invention consists ofseveral compounds, preferably of 3 to 30, more preferably of 4 to 20 andmost preferably of 4 to 16 compounds. These compounds are mixed inconventional way. As a rule, the required amount of the compound used inthe smaller amount is dissolved in the compound used in the greateramount. In case the temperature is above the clearing point of thecompound used in the higher concentration, it is particularly easy toobserve completion of the process of dissolution. It is, however, alsopossible to prepare the media by other conventional ways, e.g. using socalled pre-mixtures, which can be e.g. homologous or eutectic mixturesof compounds or using so called multi-bottle-systems, the constituentsof which are ready to use mixtures themselves.

Particularly preferred mixture concepts are indicated below: (theacronyms used are explained in Table A).

The mixtures according to the invention preferably comprise

-   -   as component A one or more compounds selected from the group of        formulae A-I to A-III, preferably        -   one or more compounds of formula A-I and one or more            compounds of formula A-II, or        -   one or more compounds of formula A-I and one or more            compounds of formula A-III, or        -   one or more compounds of formula A-II and one or more            compounds of formula A-III, or,        -   most preferred, one or more compounds of formula A-I and one            or more compounds of formula A-II and one or more compounds            of formula A-III,    -   preferably in a total concentration of 90% or less, more        preferably in the range from 60 to 90%, more preferably from 70        to 90%, and most preferably from 70 to 85% by weight of the        total mixture, preferably these compounds are selected from        -   one or more compounds of formula A-I (i.e. ether-linked            dimers), preferably in a concentration of 40% or less, more            preferably of 30% or less, based on component A,            particularly preferred one or more compounds of formula            A-I-1 to A-I-3, and especially preferred selected from the            group of formulae N-GIGIGI-O-n-O-GGG-N, in particular            N-GIGIGI-9-GGG-N, if present, preferably in            concentration >5%, in particular from 10 to 30%, based on            component A,    -   and/or        -   one or more compounds of formula A-II (i.e. methylene-linked            dimers), preferably in a concentration of 60% or less, more            preferably of 40% or less, in exceptional cases also 80 to            100% and in these cases preferably 90 to 100%, based on            component A, particularly preferred one or more compounds of            formula A-II-1 to A-II-4, and especially preferred selected            from the group of formulae F-UIZIP-n-PZU-F, preferably            FUIZIP-7-PZU-F and/or F-UIZP-9-PZU-F, preferably in            concentrations of 5% more, in particular of 10 to 20%, based            on component A,    -   and/or        -   one or more compounds of formula A-III (e.g. ester-linked            dimers), preferably in a concentration of 80% or less, more            preferably of 70% or less, based on component A,            particularly preferred one or more compounds of formula            A-III-1 to A-III-11, and especially preferred selected from            the group of formulae F-PGI-ZI-n-Z-GP-F and            F-PGI-ZI-n-Z-GP-F, preferably F-PGI-7-GP-F and/or            F-PGI-9-GP-F and/or N-PGI-7-GP-N and/or N-PGI-9-GP-N,            preferably in concentrations of 5% or more, in particular of            15 to 30% per compound, based on component A,            and/or    -   as component B one or more compounds selected from the group of        formulae B-I to B-III, preferably        -   one or more compounds of formula B-I and one or more            compounds of formula B-II, or        -   one or more compounds of formula B-I and one or more            compounds of formula B-III, or        -   one or more compounds of formula B-II and one or more            compounds of formula B-III, or        -   one or more compounds of formula B-I and one or more            compounds of formula B-II and one or more compounds of            formula B-III,    -   preferably in a total concentration of 40% or less, preferably        in the range from 5 to 40%, more preferably from 10 to 30%, and        most preferably from 10 to 20% by weight of the total mixture,        preferably these compounds are selected from formulae B-I and/or        B-II and/or B-III, and especially preferred selected from the        group of formulae PP-n-N, PPP-n-N, CC-n-V, CC-n-V1, CEPGI-n-m,        PY-n-Om, CCY-n-Om, CPY-n-Om and PYP-n-(O)m, preferably PP-5-N        and/or PPP-3-N and/or CC-3-V and/or CC-4-V and/or CC-5-V and/or        CC-3-V1 and/or CC-4-V1 and/or CEPGI-3-2 and/or CEPGI-5-2 and/or        PY-3-04, preferably in concentrations of 1% or more, in        particular in the range from 2 to 10% per compound, based on the        mixture as a whole,        and/or    -   as component C one or more chiral compounds preferably in a        total concentration in the range from 1 to 20%, in particular        from 1 to 15%, very preferably 1 to 10% by weight of the total        mixture, preferably these compounds are selected from formulae        C-I, C-I I, and C-III, in particular R-5011 or S-5011 or CD-1,        especially preferred they comprise    -   R-5011, S-5011 or CD-1, preferably in a concentration of 1% or        more, in particular 1-20%, based on the mixture as a whole        particularly preferred    -   between 1 and 3%, in particular 2%, of R-5011 or S-5011 for        displays in the ULH mode and 3.5 to 5.5%, in particular 4.5%, of        R-5011 or S-5011 for displays in the USH mode, or a another        chiral material in a concentration leading to the same        cholesteric pitch as R-5011 or S-5011 in the preferred        concentrations mentioned.

Further preferred conditions for the mesogenic media are the following.They are fulfilled independently from one another and from theconditions mentioned above. Preferably, however, two, three four or moreof these conditions and of the conditions mentioned above are fulfilledsimultaneously.

The media preferably comprise 40% or more, preferably 60% or more, basedon component B, of bimesogens comprising exactly two rings in each oftheir mesogenic groups.

The media preferably comprise one or more bimesogens comprising exactlythree rings in each of their mesogenic groups and/or one or morebimesogens comprising exactly two rings in one of their mesogenic groupsand comprising exactly three rings in their other mesogenic group.

The media preferably comprise one or more non-symmetrical bimesogens,preferably in a total concentration of 50% or more, based on componentA, preferably based on the mixture as a whole.

A further, especially preferred condition is that the mixture has a lowabsolute value of Δ∈, but preferably is dielectrically positive,especially at the temperatures between T(N,I) and 0.8 T(N,I). PreferablyΔ∈ preferably is dielectrically positive at the temperatures from T(N,I)to the temperatures at which the ULH texture is still stable, preferablyat least down to 40° C. Preferably the value of Δ∈ at these temperaturesis 3 or less, more preferably in the range from 0 or more to 2 or less.In this respect it is not very important, if the value of Δ∈ becomesnegative at lower temperatures, then it preferably is the in the rangefrom between −1 or more to 0 or less.

The bimesogenic compounds of formulae A-I, A-II and A-III and the liquidcrystalline media comprising them can be used in liquid crystaldisplays, such as STN, TN, AMD-TN, temperature compensation, guest-host,phase change or surface stabilized or polymer stabilized cholesterictexture (SSCT, PSCT) displays, in particular in flexoelectric devices,in active and passive optical elements like polarizers, compensators,reflectors, alignment layers, color filters or holographic elements, inadhesives, synthetic resins with anisotropic mechanical properties,cosmetics, diagnostics, liquid crystal pigments, for decorative andsecurity applications, in nonlinear optics, optical information storageor as chiral dopants.

The compounds of formulae A-I and/or A-II and/or A-III and the mixturesobtainable thereof are particularly useful for flexoelectric liquidcrystal display. Thus, another object of the present invention is aflexoelectric display comprising one or more compounds of formulae A-Iand/or A-II and/or A-III, or comprising a liquid crystal mediumcomprising one or more compounds of formulae A-I and/or A-II and/orA-III.

The inventive mesogenic mixtures comprising compounds of formulae A-Iand/or A-II and/or A-III can be aligned in their cholesteric phase intodifferent states of orientation by methods that are known to the expert,such as surface treatment or electric fields. For example, they can bealigned into the planar (Grandjean) state, into the focal conic state orinto the homeotropic state. Inventive compounds of formula I comprisingpolar groups with a strong dipole moment can further be subjected toflexoelectric switching, and can thus be used in electrooptical switchesor liquid crystal displays.

The switching between different states of orientation according to apreferred embodiment of the present invention is exemplarily describedbelow in detail for a sample of an inventive mixture comprisingcompounds of formulae A-I and/or A-II and/or A-III.

The total concentration of all compounds in the media according to thisapplication is 100%.

According to this preferred embodiment, the sample is placed into a cellcomprising two plane-parallel glass plates coated with electrode layers,e.g. ITO layers, and aligned in its cholesteric phase into a planarstate wherein the axis of the cholesteric helix is oriented normal tothe cell walls. This state is also known as Grandjean state, and thetexture of the sample, which is observable e.g. in a polarizationmicroscope, as Grandjean texture. Planar alignment can be achieved e.g.by surface treatment of the cell walls, for example by rubbing and/orcoating with an alignment layer such as polyimide.

A Grandjean state with a high quality of alignment and only few defectscan further be achieved by heating the sample to the isotropic phase,subsequently cooling to the chiral nematic phase at a temperature closeto the chiral nematic-isotropic phase transition, and rubbing the cell.

In the planar state, the sample shows selective reflection of incidentlight, with the central wavelength of reflection depending on thehelical pitch and the mean refractive index of the material.

When an electric field is applied to the electrodes, for example with afrequency from 10 Hz to 1 kHz, and an amplitude of up to 12 V_(rms)/μm,the sample is being switched into a homeotropic state where the helix isunwound and the molecules are oriented parallel to the field, i.e.normal to the plane of the electrodes. In the homeotropic state, thesample is transmissive when viewed in normal daylight, and appears blackwhen being put between crossed polarizers.

Upon reduction or removal of the electric field in the homeotropicstate, the sample adopts a focal conic texture, where the moleculesexhibit a helically twisted structure with the helical axis beingoriented perpendicular to the field, i.e. parallel to the plane of theelectrodes. A focal conic state can also be achieved by applying only aweak electric field to a sample in its planar state. In the focal conicstate the sample is scattering when viewed in normal daylight andappears bright between crossed polarizers.

A sample of an inventive compound in the different states of orientationexhibits different transmission of light. Therefore, the respectivestate of orientation, as well as its quality of alignment, can becontrolled by measuring the light transmission of the sample dependingon the strength of the applied electric field. Thereby it is alsopossible to determine the electric field strength required to achievespecific states of orientation and transitions between these differentstates.

In a sample of an inventive compound of formula I, the above describedfocal conic state consists of many disordered birefringent smalldomains. By applying an electric field greater than the field fornucleation of the focal conic texture, preferably with additionalshearing of the cell, a uniformly aligned texture is achieved where thehelical axis is parallel to the plane of the electrodes in large,well-aligned areas. In accordance with the literature on state of theart chiral nematic materials, such as P. Rudquist et al., Liq. Cryst. 23(4), 503 (1997), this texture is also called uniformly-lying helix (ULH)texture. This texture is required to characterize the flexoelectricproperties of the inventive compound.

The sequence of textures typically observed in a sample of an inventivecompound of formula I on a rubbed polyimide substrate upon increasing ordecreasing electric field is given below:

Starting from the ULH texture, the inventive flexoelectric compounds andmixtures can be subjected to flexoelectric switching by application ofan electric field. This causes rotation of the optic axis of thematerial in the plane of the cell substrates, which leads to a change intransmission when placing the material between crossed polarizers. Theflexoelectric switching of inventive materials is further described indetail in the introduction above and in the examples.

It is also possible to obtain the ULH texture, starting from the focalconic texture, by applying an electric field with a high frequency, offor example 10 kHz, to the sample whilst cooling slowly from theisotropic phase into the cholesteric phase and shearing the cell. Thefield frequency may differ for different compounds.

The bimesogenic compounds of formula I are particularly useful inflexoelectric liquid crystal displays as they can easily be aligned intomacroscopically uniform orientation, and lead to high values of theelastic constant k₁₁ and a high flexoelectric coefficient e in theliquid crystal medium.

The liquid crystal medium preferably exhibits a k₁₁<1×10⁻¹⁰ N,preferably <2×10⁻¹¹ N and a flexoelectric coefficient e >1×10⁻¹¹ C/m,preferably >1×10⁻¹⁰ C/m.

Apart from the use in flexoelectric devices, the inventive bimesogeniccompounds as well as mixtures thereof are also suitable for other typesof displays and other optical and electrooptical applications, such asoptical compensation or polarizing films, color filters, reflectivecholesterics, optical rotatory power and optical information storage.

A further aspect of the present invention relates to a display cellwherein the cell walls exhibit hybrid alignment conditions. The term“hybrid alignment” or orientation of a liquid crystal or mesogenicmaterial in a display cell or between two substrates means that themesogenic groups adjacent to the first cell wall or on the firstsubstrate exhibit homeotropic orientation and the mesogenic groupsadjacent to the second cell wall or on the second substrate exhibitplanar orientation.

The term “homeotropic alignment” or orientation of a liquid crystal ormesogenic material in a display cell or on a substrate means that themesogenic groups in the liquid crystal or mesogenic material areoriented substantially perpendicular to the plane of the cell orsubstrate, respectively.

The term “planar alignment” or orientation of a liquid crystal ormesogenic material in a display cell or on a substrate means that themesogenic groups in the liquid crystal or mesogenic material areoriented substantially parallel to the plane of the cell or substrate,respectively.

A flexoelectric display according to a preferred embodiment of thepresent invention comprises two plane parallel substrates, preferablyglass plates covered with a transparent conductive layer such as indiumtin oxide (ITO) on their inner surfaces, and a flexoelectric liquidcrystalline medium provided between the substrates, characterized inthat one of the inner substrate surfaces exhibits homeotropic alignmentconditions and the opposite inner substrate surface exhibits planaralignment conditions for the liquid crystalline medium.

Planar alignment can be achieved e.g. by means of an alignment layer,for example a layer of rubbed polyimide or sputtered SiO_(x), that isapplied on top of the substrate.

Alternatively it is possible to directly rub the substrate, i.e. withoutapplying an additional alignment layer. For example, rubbing can beachieved by means of a rubbing cloth, such as a velvet cloth, or with aflat bar coated with a rubbing cloth. In a preferred embodiment of thepresent invention rubbing is achieved by means of a at least one rubbingroller, like e.g. a fast spinning roller that is brushing across thesubstrate, or by putting the substrate between at least two rollers,wherein in each case at least one of the rollers is optionally coveredwith a rubbing cloth. In another preferred embodiment of the presentinvention rubbing is achieved by wrapping the substrate at leastpartially at a defined angle around a roller that is preferably coatedwith a rubbing cloth.

Homeotropic alignment can be achieved e.g. by means of an alignmentlayer coated on top of the substrate. Suitable aligning agents used onglass substrates are for example alkyltrichlorosilane or lecithine,whereas for plastic substrate thin layers of lecithine, silica or hightilt polyimide orientation films as aligning agents may be used. In apreferred embodiment of the invention silica coated plastic film is usedas a substrate.

Further suitable methods to achieve planar or homeotropic alignment aredescribed for example in J. Cognard, Mol. Cryst. Liq. Cryst. 78,Supplement 1, 1-77 (1981).

By using a display cell with hybrid alignment conditions, a very highswitching angle of flexoelectric switching, fast response times and agood contrast can be achieved.

The flexoelectric display according to present invention may alsocomprise plastic substrates instead of glass substrates. Plastic filmsubstrates are particularly suitable for rubbing treatment by rubbingrollers as described above.

Another object of the present invention is that compounds of formula I,when added to a nematic liquid crystalline mixture, produce a phasebelow the nematic.

Accordingly, the bimesogenic compounds of formula I according to thepresent invention allow the second nematic phase to be induced innematic mixtures that do not show evidence of this phase normally.Furthermore, varying the amounts of compounds of formula I allow thephase behaviour of the second nematic to be tailored to the requiredtemperature.

Examples for this are given and the mixtures obtainable thereof areparticularly useful for flexoelectric liquid crystal display. Thus,another object of the present invention is liquid crystal mediacomprising one or more compounds of formula I exhibiting a secondnematic phase.

Without further elaboration, it is believed that one skilled in the artcan, using the preceding description, utilize the present invention toits fullest extent. The following examples are, therefore, to beconstrued as merely illustrative and not limitative of the remainder ofthe disclosure in any way whatsoever.

Unless the context clearly indicates otherwise, as used herein pluralforms of the terms herein are to be construed as including the singularform and vice versa.

Throughout the description and claims of this specification, the words“comprise” and “contain” and variations of the words, for example“comprising” and “comprises”, mean “including but not limited to”, andare not intended to (and do not) exclude other components.

Throughout the present application it is to be understood that theangles of the bonds at a C atom being bound to three adjacent atoms,e.g. in a C═C or C═O double bond or e.g. in a benzene ring, are 120° andthat the angles of the bonds at a C atom being bound to two adjacentatoms, e.g. in a C≡C or in a C≡N triple bond or in an allylic positionC═C═C are 180°, unless these angles are otherwise restricted, e.g. likebeing part of small rings, like 3-, 5- or 5-atomic rings,notwithstanding that in some instances in some structural formulae theseangles are not represented exactly.

It will be appreciated that variations to the foregoing embodiments ofthe invention can be made while still falling within the scope of theinvention. Each feature disclosed in this specification, unless statedotherwise, may be replaced by alternative features serving the same,equivalent or similar purpose. Thus, unless stated otherwise, eachfeature disclosed is one example only of a generic series of equivalentor similar features.

All of the features disclosed in this specification may be combined inany combination, except combinations where at least some of suchfeatures and/or steps are mutually exclusive. In particular, thepreferred features of the invention are applicable to all aspects of theinvention and may be used in any combination. Likewise, featuresdescribed in non-essential combinations may be used separately (not incombination).

In the foregoing and in the following examples, unless otherwiseindicated, all temperatures are set forth uncorrected in degrees Celsiusand all parts and percentages are by weight.

The following abbreviations are used to illustrate the liquidcrystalline phase behavior of the compounds: K=crystalline; N=nematic;N2=second nematic; S=smectic; Ch=cholesteric; I=isotropic; Tg=glasstransition. The numbers between the symbols indicate the phasetransition temperatures in ° C.

In the present application and especially in the following examples, thestructures of the liquid crystal compounds are represented byabbreviations, which are also called “acronyms”. The transformation ofthe abbreviations into the corresponding structures is straight forwardaccording to the following three tables A to C.

All groups C_(n)H_(2n+1), C_(m)H_(2m+1), and C_(l)H2_(l+1) arepreferably straight chain alkyl groups with n, m and l C-atoms,respectively, all groups C_(n)H_(2n), C_(m)H_(2m) and C_(l)H_(2l) arepreferably (CH₂)_(n), (CH₂)_(m) and (CH₂)_(l), respectively and —CH═CH—preferably is trans-respectively E vinylene.

Table A lists the symbols used for the ring elements, table B those forthe linking groups and table C those for the symbols for the left handand the right hand end groups of the molecules.

Table D lists exemplary molecular structures together with theirrespective codes.

TABLE A Ring Elements C

P

D

DI

A

AI

G

GI

G(Cl)

GI(Cl)

G(1)

GI(1)

U

UI

Y

M

MI

N

NI

np

n3f

n3fl

th

thl

th2f

th2fl

o2f

o2fl

dh

K

KI

L

LI

F

FI

TABLE B Linking Groups n (—CH₂—)_(n) “n” is an integer except 0 and 2 E—CH₂—CH₂— V —CH═CH— T —C≡C— W —CF₂—CF₂— B —CF═CF— Z —CO—O— ZI —O—CO— X—CF═CH— XI —CH═CF— O —CH₂—O— OI —O—CH₂— Q —CF₂—O— QI —O—CF₂—

TABLE C End Groups Left hand side, used alone or Right hand side, usedalone or in combination with others in combination with others -n-C_(n)H_(2n+1)— -n —C_(n)H_(2n+1) -nO- C_(n)H_(2n+1)—O— -On—O—C_(n)H_(2n+1) -V- CH₂═CH— -V —CH═CH₂ -nV- C_(n)H_(2n+1)—CH═CH— -nV—C_(n)H_(2n)—CH═CH₂ -Vn- CH₂═CH—C_(n)H_(2n)— -Vn —CH═CH—C_(n)H_(2n+1)-nVm- C_(n)H_(2n+1)—CH═CH—C_(m)H_(2m)— -nVm—C_(n)H_(2n)—CH═CH—C_(m)H_(2m+1) -N- N≡C— -N —C≡N -S- S═C═N— -S —N═C═S-F- F— -F —F -CL- Cl— -CL —Cl -M- CFH₂— -M —CFH₂ -D- CF₂H— -D —CF₂H -T-CF₃— -T —CF₃ -MO- CFH₂O— -OM —OCFH₂ -DO- CF₂HO— -OD —OCF₂H -TO- CF₃O—-OT —OCF₃ -A- H—C≡C— -A —C≡C—H -nA- C_(n)H_(2n+1)—C≡C— -An—C≡C—C_(n)H_(2n+1) -NA- N≡C—C≡C— -AN —C≡C—C≡N Left hand side, used inRight hand side, used in combination with others only combination withothers only -...n...- —C_(n)H_(2n)— -...n... —C_(n)H_(2n)— -...M...-—CFH— -...M... —CFH— -...D...- —CF₂— -...D... —CF₂— -...V...- —CH═CH—-...V... —CH═CH— -...Z...- —CO—O— -...Z... —CO—O— -...ZI...- —O—CO—-...ZI... —O—CO— -...K...- —CO— -...K... —CO— -...W...- —CF═CF— -...W...—CF═CF—wherein n and m each are integers and three points “ . . . ” indicate aspace for other symbols of this table.

Preferably the liquid crystalline media according to the presentinvention comprise, besides the compound(s) of formula I one or morecompounds selected from the group of compounds of the formulae of thefollowing table.

TABLE D

F-PGI-O-n-O-GP-F

F-PG-O-n-O-GIP-F

N-PP-O-n-O-GU-F

F-PGI-O-n-O-PP-N

R-5011 respectively S-5011

CD-1

PP-n-N

PPP-n-N

CC-n-V

CPP-n-m

CEPGI-n-m

CPPC-n-m

PY-n-Om

CCY-n-Om

CPY-n-Om

PPY-n-Om

F-UIGI-ZI-n-Z-GU-F

N-PGI-ZI-n-Z-GP-N

F-PGI-ZI-n-Z-GP-F

N-GIGIGI-n-GGG-N

N-PGIUI-n-UGP-N

N-GIUIGI-n-GUG-N

N-GIUIP-n-PUG-N

N-PGI-n-GP-N

N-PUI-n-UP-N

N-UIUI-n-UU-N

N-GIGI-n-GG-N

F-UIGI-n-GU-F

UIP-n-PU

N-PGI-n-GP-N

N-PGI-ZI-n-Z-GP-N

F-PGI-ZI-n-Z-GP-F

F-UIGI-ZI-n-Z-GU-F

F-PGI-ZI-n-Z-PP-N

F-PGI-ZI-n-Z-PUU-N

F-PGI-ZI-n-Z-GUU-N

N-GIGI-n-GG-N

N-PUI-n-UP-N

N-PUI-n-UP-N

F-UIP-ZI-n-Z-PZU-F

MIXTURE EXAMPLES Mixture Example 1 Mixture M1

Composition Compound No. Abbreviation Conc./% 1 R-5011 2.0 2F-PGI-ZI-7-Z-PP-N 29.0 3 F-PGI-ZI-9-Z-PUU-N 29.0 4 N-PGI-ZI-7-Z-GP-N15.0 5 F-UIZIP-7-PZU-F 15.0 6 CC-3-V 5.0 7 PPP-3-N 5.0 Σ 100.0

This mixture is particularly well suitable for the ULH-mode. It isinvestigated in antiparallel rubbed cells with polyimide orientationlayers (e.g. AL3046) of appropriate cell gap, typically of 5.4 μm.

It has a range of the (chiral) nematic phase from 20° C. to 90° C. Thecholesteric pitch (P) is 300 nm and the flexoelectric ratio (e/K) is 3.6V⁻¹, both determined at a temperature of 35° C. The electric field hasbeen varied from 0 V/μm) to about 3.0 V/μm), leading to a tilt angle (Θ)increasing from 0° to about 27.5° over that range of electric fields.

It has a double response time for switching on (T_(on)) of about 1 ms atan electric field of 3.0 V/μm and of about 0.5 ms at an electric fieldof 3.5 V/μm. I.e. the sum of the response times(τ_(on,driven)+τ_(off,driven)) is below 1 ms at electrical fields of 3.0V/μm and more. The sum of the response times for switching off byrelaxation only (τ_(on,driven)+τ_(off,driven)) is below 5 ms atelectrical fields of 3.0 V/μm and more. Here the double of the responsetime for switching on (τ_(on)) is the decisive feature for severalapplications, as the mixture can be actively switched on as well as off.

The transmission under crossed polarizers of this mixture relative to anempty cell (for reference of 100%) has a maximum value switched at anelectric field of 3.0 V/μm with 60%. At an electric field of 3.5 V/μmthe relative transmission of this mixture is about 58%. Probably themaximum the transmission is limited by the insufficient alignment of thehelix: some of the ULH is at an undesired angle to the directionrequired.

Mixture Example 2 and Comparative Mixture Example 2 Comparative MixtureExample 2 Mixture C2

Composition Compound No. Abbreviation Conc./% 1 R-5011 2.0 2F-PGI-ZI-7-Z-PP-N 29.6 3 F-PGI-ZI-9-Z-PP-N 19.4 4 F-UIGI-ZI-9-Z-GP-N31.6 5 F-PGI-ZI-9-Z-PUU-N 17.4 Σ 100.0

This comparative mixture is investigated as described under mixtureexample 1.

It has a range of the (chiral) nematic phase from below 20° C. to 97° C.The cholesteric pitch (P) is 310 nm and the flexoelectric ratio (e/K) is4.41 V⁻¹, both determined at a temperature of 35° C. The total responsetime for switching driven both on and off (τ_(on,driven)+τ_(off,driven))is 3.9 ms at an electric field of 3.33 V/μm.

Mixture Example 2 Mixture M2

10% of the following mixture (mixture N1),

Composition Compound No. Abbreviation Conc./% 1 PY-3-O2 14.5 2 CCY-3-O23.5 3 CCY-4-O2 13.5 4 CPY-2-O2 11.0 5 CPY-3-O2 11.0 6 CC-3-V 29.0 7CPP-3-2 13.5 5 CPPC-3-3 4.0 Σ 100.0which has the following physical properties:

T_(N,I)=103.6 C;

Δn=0.124 @25 C;

Δ∈=−2.8 @25 C; and

γ₁=114 mPa·s,are added to 90% of the mixture C2 of the respective comparativeexample.

The resultant mixture (M2) is investigated as described under mixtureexample 1. It has a range of the (chiral) nematic phase from 2° C. to102° C. The cholesteric pitch (P) is 363 nm and the flexoelectric ratio(e/K) is 3.21 V⁻¹, both determined at a temperature of 35° C. The totalresponse time (τ_(on,driven)+τ_(off,driven)) is 2 ms and the totalresponse time (τ_(on,driven)+τ_(off,driven)) is 6 ms (τ_(on,driven)=1 msand τ_(off,driven)=5.2 ms), all at an electric field of 3.33 V/μm.

Mixture Example 3 and Comparative Mixture Example 3 Comparative MixtureExample 3 Mixture C3

Composition Compound No. Abbreviation Conc./% 1 R-5011 1.8 2N-GIGI-ZI-9-Z-GG-N 8.5 3 N-PGI-ZI-9-Z-GP-N 8.5 4 F-PGI-ZI-9-Z-GP-F 16.85 F-UIGI-ZI-9-Z-GP-N 22.6 6 F-PGI-ZI-9-Z-PUU-N 8.4 7 N-GIGI-9-GG-N 25.18 N-UIUI-9-UU-N 8.4 Σ 100.0

This comparative mixture is investigated as described under mixtureexamples 1 and 2.

It has a clearing point from the (chiral) nematic phase of 64° C. Thecholesteric pitch (P) is 348 nm and the flexoelectric ratio (e/K) is 5.2V⁻¹, both determined at a temperature of 35° C. The total response time(τ_(on,driven)+τ_(off,driven)) is 8.4 ms at an electric field of 3.33V/μm.

Mixture Example 3 Mixture M3

10% of the following binary mixture (mixture N2),

Composition Compound No. Abbreviation Conc./% 1 PP-5-N 50.0 2 PPP-5-N50.0 Σ 100.0are added to 90% of the mixture C3 of the respective comparativeexample.

The resultant mixture (M3) is investigated as described under mixtureexamples 1 and 2. It has a clearing point from the (chiral) nematicphase of 70° C. The cholesteric pitch (P) is 283 nm and theflexoelectric ratio (e/K) is 3.7 V⁻¹, both determined at a temperatureof 35° C. The total response time (τ_(on,driven)+τ_(off,driven)) is 5.5m sat an electric field of 3.33 V/μm.

Mixture Example 4 Mixture M4

Composition Compound No. Abbreviation Conc./% 1 R-5011 2.0 2N-PGI-ZI-9-Z-PUU-N 25.0 3 N-PGI-ZI-7-Z-GP-N 9.0 4 N-PGI-ZI-9-Z-GP-N 15.05 F-GIP-ZI-9-Z-PG-F 10.0 6 F-UIGI-ZI-9-Z-GP-N 15.0 7 TO-GIGI-ZI-9-Z-GP-N9.0 8 CC-3-V 7.5 9 PYP-2-3 7.5 Σ 100.0

This mixture is investigated as described under mixture example 1.

Mixture Example 5 Mixture M5

Composition Compound No. Abbreviation Conc./% 1 R-5011 2.0 2F-PGI-O-9-O-GP-F 16.0 3 F-PG-O-9-O-PP-N 21.4 4 F-PI-ZI-7-Z-PP-N 12.7 5F-PI-ZI-9-Z-PP-N 10.4 6 N-GIGI-ZI-9-Z-GG-N 8.0 7 F-UIGI-ZI-9-Z-GP-N 9.58 CP-3-N 1.4 9 CY-3-O2 1.3 10 PGIGI3-F 2.0 11 CP-3-O1 2.2 12 PTP-1-O20.7 13 CCG-V-F 1.0 14 PPTUI-3-2 4.0 15 PPTUI-3-4 7.4 Σ 100.0

This mixture is investigated as described under mixture example 1.

Mixture Example 6 Mixture M6

Composition Compound No. Abbreviation Conc./% 1 R-5011 2.0 2N-PGI-ZI-9-Z-PUU-N 25.0 3 N-PGI-ZI-9-Z-GP-N 15.0 4 N-PGI-ZI-7-Z-GP-N 9.05 F-GIP-ZI-9-Z-PG-F 10.0 6 F-UIGI-ZI-9-Z-GP-N 15.0 7 TO-GIGI-ZI-9-Z-GP-N9.0 8 CC-3-V 5.0 9 PYP-2-3 5.0 Σ 100.0

This mixture is investigated as described under mixture example 1.

1. Mesogenic medium comprising a first component, component A,consisting of bimesogenic compounds selected from the group of compoundsof formulae A-I to A-III

wherein R¹¹ and R¹², R²¹ and R²² and R³¹ and R³² are each independentlyH, F, Cl, CN, NCS or a straight-chain or branched alkyl group with 1 to25 C atoms which may be unsubstituted, mono- or polysubstituted byhalogen or CN, it being also possible for one or more non-adjacent CH₂groups to be replaced, in each occurrence independently from oneanother, by —O—, —S—, —NH—, —N(CH₃)—, —CO—, —COO—, —OCO—, —O—CO—O—,—S—CO—, —CO—S—, —CH═CH—, —CH═CF—, —CF═CF— or —C≡C— in such a manner thatoxygen atoms are not linked directly to one another, MG¹¹ and MG¹², MG²¹and MG²² and MG³¹ and MG³² are each independently a mesogenic group,Sp¹, Sp² and Sp³ are each independently a spacer group comprising 5 to40 C atoms, wherein one or more non-adjacent CH₂ groups, with theexception of the CH₂ groups of Sp¹ linked to O-MG¹¹ and/or O-MG¹², ofSp² linked to MG²¹ and/or MG²² and of Sp³ linked to X³¹ and X³², mayalso be replaced by —O—, —S—, —NH—, —N(CH₃)—, —CO—, —O—CO—, —S—CO—,—O—COO—, —CO—S—, —CO—O—, —CH(halogen)-, —CH(CN)—, —CH═CH— or —C≡C—,however in such a way that (in the molecules) no two O-atoms areadjacent to one another, no two —CH═CH— groups are adjacent to eachother, and no two groups selected from —O—CO—, —S—CO—, —O—COO—, —CO—S—,—CO—O— and —CH═CH— are adjacent to each other and X³¹ and X³² areindependently from one another a linking group selected from —CO—O—,—O—CO—, —CH═CH—, —C≡C— or —S—, and, alternatively, one of them may alsobe either —O— or a single bond, and, again alternatively, one of themmay be —O— and the other one a single bond, a second component,component B, consisting of nematogenic compounds, preferably selectedfrom the group of compounds of formulae B-I to B-III

wherein R^(B1), RB²¹ and RB²² and RB³¹ and RB³² are each independentlyH, F, Cl, CN, NCS or a straight-chain or branched alkyl group with 1 to25 C atoms which may be unsubstituted, mono- or polysubstituted byhalogen or CN, it being also possible for one or more non-adjacent CH₂groups to be replaced, in each occurrence independently from oneanother, by —O—, —S—, —NH—, —N(CH₃)—, —CO—, —COO—, —OCO—, —O—CO—O—,—S—CO—, —CO—S—, —CH═CH—, —CH═CF—, —CF═CF— or —C≡C— in such a manner thatoxygen atoms are not linked directly to one another, X^(B1) is F, Cl,CN, NCS, preferably CN, Z^(B1), Z^(B2) and Z^(B3) are in each occurrenceindependently —CH₂—CH₂—, —CO—O—, —O—CO—, —CF₂—O—, —O—CF₂—, —CH═CH— or asingle bond,

and

are in each occurrence independently

or

alternatively one or more of are

and n is 1, 2 or 3, and a third component, component C, consisting ofone or more chiral molecules.
 2. Mesogenic medium according to claim 1comprising one or more compounds selected from formulae A-I to A-III,characterized in that MG¹¹ and MG¹², MG²¹ and MG²² and MG³¹ and MG³² areindependently of each other selected of formula II-A¹-(Z¹-A²)_(m)-  II wherein Z¹ is —COO—, —OCO—, —O—CO—O—, —OCH₂—,—CH₂O—, —CH₂CH₂—, —(CH₂)₄—, —CF₂CF₂—, —CH═CH—, —CF═CF—, —CH═CH—COO—,—OCO—CH═CH—, —C≡C— or a single bond, A¹ and A² are each independently ineach occurrence 1,4-phenylene, wherein in addition one or more CH groupsmay be replaced by N,trans-1,4-cyclohexylene in which, in addition, oneor two non-adjacent CH₂ groups may be replaced by O and/or S,1,4-cyclohexenylene, 1,4-bicyclo-(2,2,2)-octylene, piperidine-1,4-diyl,naphthalene-2,6-diyl, decahydro-naphthalene-2,6-diyl,1,2,3,4-tetrahydro-naphthalene-2,6-diyl, cyclobutane-1,3-diyl,spiro[3.3]heptane-2,6-diyl or dispiro[3.1.3.1]decane-2,8-diyl, it beingpossible for all these groups to be unsubstituted, mono-, di-, tri- ortetrasubstituted with F, Cl, CN or alkyl, alkoxy, alkylcarbonyl oralkoxycarbonyl groups with 1 to 7 C atoms, wherein one or more H atomsmay be substituted by F or Cl, m is 0, 1, 2 or
 3. 3. Mesogenic mediumaccording to claim 1 comprising one or more compounds selected fromformulae A-I to A-III, characterized in that MG¹¹ and MG¹², MG²¹ andMG²² and MG³¹ and MG³² are each and independently selected of thefollowing formulae and their mirror images

wherein L is in each occurrence independently of each other F, Cl, CN,OH, NO₂ or an optionally fluorinated alkyl, alkoxy or alkanoyl groupwith 1 to 7 C atoms, and r is in each occurrence independently of eachother 0, 1, 2, 3 or
 4. 4. Mesogenic medium according to claim 1,characterized in that it comprises one or more compounds of formula A-I.5. Mesogenic medium according to claim 1, characterized in that itcomprises one or more compounds of formula A-II.
 6. Mesogenic mediumaccording to claim 1, characterized in that it comprises one or morecompounds of formula A-III.
 7. Mesogenic medium according to claim 1,characterized in that it comprises one or more compounds of formula B-I.8. Mesogenic medium according to claim 1, characterized in that itcomprises one or more compounds of formula B-II.
 9. Mesogenic mediumaccording to claim 1, characterized in that it comprises one or morecompounds of formula B-III.
 10. Mesogenic medium according to claim 1,characterized in that it comprises component B, consisting of compoundsselected from the group of formulae B-I to B-III in a concentration 40%or less based on the medium as a whole.
 11. Mesogenic medium accordingto claim 1, characterized in that it exhibits a second nematic phase.12. (canceled)
 13. Liquid crystal device comprising a mesogenic mediumaccording to claim
 1. 14. Liquid crystal device according to claim 13,characterized in that it is a flexoelectric device.
 15. Liquid crystaldevice according to claim 13, characterized in that it comprises twoplane parallel electrodes the inner surfaces of which exhibit planar,anti-parallel alignment conditions.